This commit introduces settings version to index metadata. This value is
monotonically increasing and is updated on settings updates. This will
be useful in cross-cluster replication so that we can request settings
updates from the leader only when there is a settings update.

* elastic/master:
  Mute PartitionedRoutingIT#testShrinking on Windows
  Mute testToQuery test
  [TEST] Make sure there are shards started so that `ESIntegTestCase#assertSameDocIdsOnShards()` does not fail with shard not found.
  Change shard changes api's threadpool from get to search (elastic#34421)
  Update TESTING.asciidoc title (elastic#34401)
  Tests: Fix DateFormatter equals tests with locale (elastic#34435)
  Docs: Remove unnecessary qualifier from wildcard import note (elastic#34419)
  CCR/TEST: AwaitsFix testFailOverOnFollower
  [Painless] Add a Map for java names to classes for use in the custom classloader (elastic#34424)
  TEST: Fix indentation in FullClusterRestartIT (elastic#34420)
  [WIP] Ingest Attachement: Upgrade tika to v1.19.1 (elastic#33896)
  NETWORKING: Upgrade Netty to 4.1.30 (elastic#34417)
  Allow an AuthenticationResult to return metadata (elastic#34382)
  [ML] Add an ingest pipeline definition to structure finder (elastic#34350)
  Handle pre-6.x time fields (elastic#34373)
  ListenableFuture should preserve ThreadContext (elastic#34394)

* master:
  Do not update number of replicas on no indices (elastic#34481)
  Core: Remove two methods from AbstractComponent (elastic#34336)
  Use RoleRetrievalResult for better caching (elastic#34197)
  Revert "Search: Fix spelling mistake in Javadoc (elastic#34480)"
  Search: Fix spelling mistake in Javadoc (elastic#34480)
  Docs: improve formatting of Query String Query doc page (elastic#34432)
  Tests: Handle epoch date formatters edge cases (elastic#34437)
  Test: Fix running with external cluster
  Fix handling of empty keyword in terms aggregation (elastic#34457)
  [DOCS] Fix tag in SecurityDocumentationIT
  [Monitoring] Add additional necessary mappings for apm-server (elastic#34392)
  SCRIPTING: Move Aggregation Script Context to its own class (elastic#33820)
  MINOR: Remove Deadcode in  ExpressionTermSetQuery (elastic#34442)
  HLRC: Get SSL Certificates API (elastic#34135)