* master:
  Add get field mappings to High Level REST API Client (#31423)
  [DOCS] Updates Watcher examples for code testing (#31152)
  TEST: Add bwc recovery tests with synced-flush index
  [DOCS] Move sql to docs (#31474)
  [DOCS] Move monitoring to docs folder (#31477)
  Core: Combine doExecute methods in TransportAction (#31517)
  IndexShard should not return null stats (#31528)
  fix repository update with the same settings but different type (#31458)
  Fix Mockito trying to mock IOException that isn't thrown by method (#31433) (#31527)
  Node selector per client rather than per request (#31471)
  Core: Combine messageRecieved methods in TransportRequestHandler (#31519)
  Upgrade to Lucene 7.4.0. (#31529)
  [ML] Add ML filter update API (#31437)
  Allow multiple unicast host providers (#31509)
  Avoid deprecation warning when running the ML datafeed extractor. (#31463)
  REST high-level client: add simulate pipeline API (#31158)
  Get Mapping API to honour allow_no_indices and ignore_unavailable (#31507)
  [PkiRealm] Invalidate cache on role mappings change (#31510)
  [Security] Check auth scheme case insensitively (#31490)
  In NumberFieldType equals and hashCode, make sure that NumberType is taken into account. (#31514)
  [DOCS] Fix REST tests in SQL docs
  [DOCS] Add code snippet testing in more ML APIs (#31339)
  Core: Remove ThreadPool from base TransportAction (#31492)
  [DOCS] Remove fixed file from build.gradle
  Rename createNewTranslog to fileBasedRecovery (#31508)
  Test: Skip assertion on windows
  [DOCS] Creates field and document level security overview (#30937)
  [DOCS] Significantly improve SQL docs
  [DOCS] Move migration APIs to docs (#31473)
  Core: Convert TransportAction.execute uses to client calls (#31487)
  Return transport addresses from UnicastHostsProvider (#31426)
  Ensure local addresses aren't null (#31440)
  Remove unused generic type for client execute method (#31444)
  Introduce http and tcp server channels (#31446)