Feat/Add support for runtime_mappings [Issue: #152]

[atreids]

Issue:

resolves #152

Additional Author

Original PR was raised by @jmaitrehenry but appears to be abandoned. This PR attempts to complete implementation of this feature, based upon his original work.

Aim:

Add support for Elasticsearch runtime_mappings field, added in v7.11.0.

Usage:

const field = esb.runtimeField(
      'keyword',
      `emit(doc['sessionId'].value + '::' + doc['name'].value)`,
);
const reqBody = esb.requestBodySearch();
reqBody.runtimeMapping('sessionId-eventName', field);

Will generate query:

{
  "runtime_mappings": {
    "sessionId-eventName": {
      "type": "keyword",
      "script": {
        "source": "emit(doc['sessionId'].value + '::' + doc['name'].value)"
      }
    }
  }
}

Changes from original PR

• Removed name property from RuntimeField class. It, as far as I could tell, didn't do anything. The name for the runtime field is set as the first param of runtimeMapping.
• Updated and expanded JSDocs.
• Expanded typing.
• Renamed some variables.

[sudo-suhas]

Thanks again @atreids for the PR!

[github-actions]

🎉 This PR is included in version 2.28.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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