Support writing to elastic data streams

[jeremyross]

Currently micrometer cannot write to elastic data streams because micrometer uses the index operation.

From the docs:

A data stream lets you store append-only time series data across multiple indices while giving you a single named resource for requests. Data streams are well-suited for logs, events, metrics, and other continuously generated data.

Data streams have been out for a while now and are the preferred mechanism for write-only, time series data because they support Index Lifecycle Management, which provides automation around index management.

The current barrier to micrometer writing to data streams is that requests must use an op_type of create

Luckily this is a simple change. Currently micrometer uses the index operation, which is analogous to a PUT or upsert. Semantically speaking, the create operation is a better fit since micrometer should always be creating new documents. So, the solution is to use the create operation, which is a better semantic fit and works with data streams.

[jeremyross]

This also solves the root issue behind #2255.

[jeremyross]

This also solves the inevitable roadblock users would hit after #2705 is solved. See this comment.