Deprecate the document create endpoint.

[jtibshirani]

The following updates were made:

• Introduce the endpoint {index}/_create/{id} to replace {index}/{type}/{id}/_create.
• Add deprecation warnings to RestIndexAction, plus tests in RestIndexActionTests.
• For each REST yml test, create one version without types, and another legacy version that retains types (called *_with_types.yml).
• Update HLRC request conversion to use the new endpoint when no type is provided. No updates were made to HLRC requests and responses, because this API reuses IndexRequest/ IndexResponse.

[elasticmachine]

Pinging @elastic/es-search

[mayya-sharipova]

@jtibshirani Thanks Julie, nice work!