* 6.x: (25 commits)
  Backport of types removal for Put/Get index templates (elastic#38465)
  Add support for API keys to access Elasticsearch (elastic#38291) (elastic#38399)
  Deprecate support for internal versioning for concurrency control (elastic#38451)
  Deprecate types in rollover index API (elastic#38389) (elastic#38458)
  Add typless client side GetIndexRequest calls and response class (elastic#38422)
  [ML] Report index unavailable instead of waiting for lazy node (elastic#38444)
  await fix CurtIT#testIndex until elastic#38451 is merged (elastic#38466)
  Update ilm-api.asciidoc, point to REMOVE policy (elastic#38235) (elastic#38464)
  SQL: Fix esType for DATETIME/DATE and INTERVALS (elastic#38179)
  Clean up duplicate follow config parameter code (elastic#37688) (elastic#38443)
  Deprecation check for No Master Block setting (elastic#38383)
  Bubble-up exceptions from scheduler (elastic#38441)
  Lift retention lease expiration to index shard (elastic#38391)
  Deprecate maxRetryTimeout in RestClient and increase default value (elastic#38425)
  Update Rollup Caps to allow unknown fields (elastic#38446)
  Backport of elastic#38411: `if_seq_no` and `if_primary_term` parameters aren't wired correctly in REST Client's CRUD API
  Support unknown fields in ingest pipeline map configuration (elastic#38429)
  SQL: Implement CURRENT_DATE (elastic#38175)
  Backport changes to the release notes script. (elastic#38346)
  Fix ILM explain response to allow unknown fields (elastic#38363)
  ...