I would like to be able to perform bulk reindex requests and also specify a pipeline. The pipeline blanks out some fields and adds another indicating that this action has been taken. Due to security concerns, scripting is not an option.

The destination indices will only contain document such that they have gone through the pipeline.

I know that there's no way to do this with the Java client (one can bulk reindex but can't specify a pipeline), but what about in the REST API?

e.g. to perform the reindexes at the bottom here in bulk (the assumption is that there will be millions of values for `message_id` that will be provided from elsewhere):

```
#Create some data:
POST /mytestindex/message
{
  "message_id": "123-456-789",
  "body": "this is some text"
}

POST /mytestindex/message
{
  "message_id": "234-567-890",
  "body": "this is also some text"
}

#Create a pipeline to blank out the body field 
PUT /_ingest/pipeline/my-test-pipeline
{
  "description": "my test pipeline",
  "processors": [{
    "set": {
      "field": "body",
      "value": ""
    }
  }]
}

#reindex by message_id:
POST _reindex
{
  "source": {
    "index": "mytestindex",
    "query": {
      "match": {
        "message_id": "123-456-789"
      }
    }
  },
  "dest": {
    "index": "mytestindex_new",
    "pipeline": "my-test-pipeline"
  }
}

POST _reindex
{
  "source": {
    "index": "mytestindex",
    "query": {
      "match": {
        "message_id": "234-567-890"
      }
    }
  },
  "dest": {
    "index": "mytestindex_new",
    "pipeline": "my-test-pipeline"
  }
}

```