We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Use Full URL for ImageRenditionField.
### Is your proposal related to a problem?

<!--
  Provide a clear and concise description of what the problem is.
  For example, "I'm always frustrated when..."
-->

I'm a big fan of the new `full_url` field that images have and would like them to be easily used in the API.

Assuming one's frontend app is living on a different domain to the Wagtail API then the default relative URLs aren't as useful.

### Describe the solution you'd like

<!--
  Provide a clear and concise description of what you want to happen.
-->

Add `full_url` to the output of `ImageRenditionField`.

I propose it just replace the `url` field altogether, but both could be returned.

### Describe alternatives you've considered

<!--
  Let us know about other solutions you've tried or researched.
-->

I've been extending the `ImageRenditionField` for use in my own projects

### Additional context

<!--
  Is there anything else you can add about the proposal?
  You might want to link to related issues here, if you haven't already.
-->

(Write your answer here.)

Use Full URL for ImageRenditionField.
### Is your proposal related to a problem?

<!--
  Provide a clear and concise description of what the problem is.
  For example, "I'm always frustrated when..."
-->

I'm a big fan of the new `full_url` field that images have and would like them to be easily used in the API.

Assuming one's frontend app is living on a different domain to the Wagtail API then the default relative URLs aren't as useful.

### Describe the solution you'd like

<!--
  Provide a clear and concise description of what you want to happen.
-->

Add `full_url` to the output of `ImageRenditionField`.

I propose it just replace the `url` field altogether, but both could be returned.

### Describe alternatives you've considered

<!--
  Let us know about other solutions you've tried or researched.
-->

I've been extending the `ImageRenditionField` for use in my own projects

### Additional context

<!--
  Is there anything else you can add about the proposal?
  You might want to link to related issues here, if you haven't already.
-->

(Write your answer here.)


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `wagtail/images/api/fields.py`
Content:
```
1 from collections import OrderedDict
2 
3 from rest_framework.fields import Field
4 
5 from ..models import SourceImageIOError
6 
7 
8 class ImageRenditionField(Field):
9     """
10     A field that generates a rendition with the specified filter spec, and serialises
11     details of that rendition.
12 
13     Example:
14     "thumbnail": {
15         "url": "/media/images/myimage.max-165x165.jpg",
16         "width": 165,
17         "height": 100,
18         "alt": "Image alt text"
19     }
20 
21     If there is an error with the source image. The dict will only contain a single
22     key, "error", indicating this error:
23 
24     "thumbnail": {
25         "error": "SourceImageIOError"
26     }
27     """
28 
29     def __init__(self, filter_spec, *args, **kwargs):
30         self.filter_spec = filter_spec
31         super().__init__(*args, **kwargs)
32 
33     def to_representation(self, image):
34         try:
35             thumbnail = image.get_rendition(self.filter_spec)
36 
37             return OrderedDict(
38                 [
39                     ("url", thumbnail.url),
40                     ("width", thumbnail.width),
41                     ("height", thumbnail.height),
42                     ("alt", thumbnail.alt),
43                 ]
44             )
45         except SourceImageIOError:
46             return OrderedDict(
47                 [
48                     ("error", "SourceImageIOError"),
49                 ]
50             )
51
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/wagtail/images/api/fields.py b/wagtail/images/api/fields.py
--- a/wagtail/images/api/fields.py
+++ b/wagtail/images/api/fields.py
@@ -13,6 +13,7 @@
     Example:
     "thumbnail": {
         "url": "/media/images/myimage.max-165x165.jpg",
+        "full_url": "https://media.example.com/media/images/myimage.max-165x165.jpg",
         "width": 165,
         "height": 100,
         "alt": "Image alt text"
@@ -37,6 +38,7 @@
             return OrderedDict(
                 [
                     ("url", thumbnail.url),
+                    ("full_url", thumbnail.full_url),
                     ("width", thumbnail.width),
                     ("height", thumbnail.height),
                     ("alt", thumbnail.alt),

{"golden_diff": "diff --git a/wagtail/images/api/fields.py b/wagtail/images/api/fields.py\n--- a/wagtail/images/api/fields.py\n+++ b/wagtail/images/api/fields.py\n@@ -13,6 +13,7 @@\n     Example:\n     \"thumbnail\": {\n         \"url\": \"/media/images/myimage.max-165x165.jpg\",\n+        \"full_url\": \"https://media.example.com/media/images/myimage.max-165x165.jpg\",\n         \"width\": 165,\n         \"height\": 100,\n         \"alt\": \"Image alt text\"\n@@ -37,6 +38,7 @@\n             return OrderedDict(\n                 [\n                     (\"url\", thumbnail.url),\n+                    (\"full_url\", thumbnail.full_url),\n                     (\"width\", thumbnail.width),\n                     (\"height\", thumbnail.height),\n                     (\"alt\", thumbnail.alt),\n", "issue": "Use Full URL for ImageRenditionField.\n### Is your proposal related to a problem?\r\n\r\n<!--\r\n  Provide a clear and concise description of what the problem is.\r\n  For example, \"I'm always frustrated when...\"\r\n-->\r\n\r\nI'm a big fan of the new `full_url` field that images have and would like them to be easily used in the API.\r\n\r\nAssuming one's frontend app is living on a different domain to the Wagtail API then the default relative URLs aren't as useful.\r\n\r\n### Describe the solution you'd like\r\n\r\n<!--\r\n  Provide a clear and concise description of what you want to happen.\r\n-->\r\n\r\nAdd `full_url` to the output of `ImageRenditionField`.\r\n\r\nI propose it just replace the `url` field altogether, but both could be returned.\r\n\r\n### Describe alternatives you've considered\r\n\r\n<!--\r\n  Let us know about other solutions you've tried or researched.\r\n-->\r\n\r\nI've been extending the `ImageRenditionField` for use in my own projects\r\n\r\n### Additional context\r\n\r\n<!--\r\n  Is there anything else you can add about the proposal?\r\n  You might want to link to related issues here, if you haven't already.\r\n-->\r\n\r\n(Write your answer here.)\r\n\nUse Full URL for ImageRenditionField.\n### Is your proposal related to a problem?\r\n\r\n<!--\r\n  Provide a clear and concise description of what the problem is.\r\n  For example, \"I'm always frustrated when...\"\r\n-->\r\n\r\nI'm a big fan of the new `full_url` field that images have and would like them to be easily used in the API.\r\n\r\nAssuming one's frontend app is living on a different domain to the Wagtail API then the default relative URLs aren't as useful.\r\n\r\n### Describe the solution you'd like\r\n\r\n<!--\r\n  Provide a clear and concise description of what you want to happen.\r\n-->\r\n\r\nAdd `full_url` to the output of `ImageRenditionField`.\r\n\r\nI propose it just replace the `url` field altogether, but both could be returned.\r\n\r\n### Describe alternatives you've considered\r\n\r\n<!--\r\n  Let us know about other solutions you've tried or researched.\r\n-->\r\n\r\nI've been extending the `ImageRenditionField` for use in my own projects\r\n\r\n### Additional context\r\n\r\n<!--\r\n  Is there anything else you can add about the proposal?\r\n  You might want to link to related issues here, if you haven't already.\r\n-->\r\n\r\n(Write your answer here.)\r\n\n", "before_files": [{"content": "from collections import OrderedDict\n\nfrom rest_framework.fields import Field\n\nfrom ..models import SourceImageIOError\n\n\nclass ImageRenditionField(Field):\n    \"\"\"\n    A field that generates a rendition with the specified filter spec, and serialises\n    details of that rendition.\n\n    Example:\n    \"thumbnail\": {\n        \"url\": \"/media/images/myimage.max-165x165.jpg\",\n        \"width\": 165,\n        \"height\": 100,\n        \"alt\": \"Image alt text\"\n    }\n\n    If there is an error with the source image. The dict will only contain a single\n    key, \"error\", indicating this error:\n\n    \"thumbnail\": {\n        \"error\": \"SourceImageIOError\"\n    }\n    \"\"\"\n\n    def __init__(self, filter_spec, *args, **kwargs):\n        self.filter_spec = filter_spec\n        super().__init__(*args, **kwargs)\n\n    def to_representation(self, image):\n        try:\n            thumbnail = image.get_rendition(self.filter_spec)\n\n            return OrderedDict(\n                [\n                    (\"url\", thumbnail.url),\n                    (\"width\", thumbnail.width),\n                    (\"height\", thumbnail.height),\n                    (\"alt\", thumbnail.alt),\n                ]\n            )\n        except SourceImageIOError:\n            return OrderedDict(\n                [\n                    (\"error\", \"SourceImageIOError\"),\n                ]\n            )\n", "path": "wagtail/images/api/fields.py"}], "after_files": [{"content": "from collections import OrderedDict\n\nfrom rest_framework.fields import Field\n\nfrom ..models import SourceImageIOError\n\n\nclass ImageRenditionField(Field):\n    \"\"\"\n    A field that generates a rendition with the specified filter spec, and serialises\n    details of that rendition.\n\n    Example:\n    \"thumbnail\": {\n        \"url\": \"/media/images/myimage.max-165x165.jpg\",\n        \"full_url\": \"https://media.example.com/media/images/myimage.max-165x165.jpg\",\n        \"width\": 165,\n        \"height\": 100,\n        \"alt\": \"Image alt text\"\n    }\n\n    If there is an error with the source image. The dict will only contain a single\n    key, \"error\", indicating this error:\n\n    \"thumbnail\": {\n        \"error\": \"SourceImageIOError\"\n    }\n    \"\"\"\n\n    def __init__(self, filter_spec, *args, **kwargs):\n        self.filter_spec = filter_spec\n        super().__init__(*args, **kwargs)\n\n    def to_representation(self, image):\n        try:\n            thumbnail = image.get_rendition(self.filter_spec)\n\n            return OrderedDict(\n                [\n                    (\"url\", thumbnail.url),\n                    (\"full_url\", thumbnail.full_url),\n                    (\"width\", thumbnail.width),\n                    (\"height\", thumbnail.height),\n                    (\"alt\", thumbnail.alt),\n                ]\n            )\n        except SourceImageIOError:\n            return OrderedDict(\n                [\n                    (\"error\", \"SourceImageIOError\"),\n                ]\n            )\n", "path": "wagtail/images/api/fields.py"}]}