Support to runtime_mappings

[sanvir10]

In the doc page i can't see if this support add runtime_mappings in the query body:

Example:

{
  "runtime_mappings": {
    "duration": {
      "type": "long",
      "script": {
        "source": "emit(doc['measures.end'].value - doc['measures.start'].value);"
      }
    }
  },
  "aggs": {
    "duration_stats": {
      "stats": {
        "field": "duration"
      }
    }
  }
}

Ref: https://www.elastic.co/guide/en/elasticsearch/reference/7.x/runtime-search-request.html

[sudo-suhas]

This is not supported as of now. PRs are welcome.