title: How to rename field names while Indexing a document in ElasticSearch
body: <p>I have a JSON object with some of the fields like this:-</p>
  
  <pre><code>{
      "desc": "this is test description",
      "name": "some random name",
  }
  </code></pre>
  
  <p>While indexing this document, I would like to change the field names and my document after indexing should look like this:-</p>
  
  <pre><code>{
      "description": "this is test description",
      "user_name": "some random name",
  }
  </code></pre>
  
  <p>I've read about the Ingest pipeline processor but they only rename after a field is created. Is there any way that I could change the field names while indexing?</p>