Rather than scheduling pings to the leader index when we are caught up
to the leader, this commit introduces long polling for changes. We will
fire off a request to the leader which if we are already caught up will
enter a poll on the leader side to listen for global checkpoint
changes. These polls will timeout after a default of one minute, but can
also be specified when creating the following task. We use these time
outs as a way to keep statistics up to date, to not exaggerate time
since last fetches, and to avoid pipes being broken.

…polling

* elastic/master:
  SQL: Return correct catalog separator in JDBC (elastic#33670)
  [CCR] Add validation for max_retry_delay (elastic#33648)
  [CCR] Add monitoring mapping verification test (elastic#33662)
  CORE: Disable Setting Type Validation (elastic#33660) (elastic#33669)
  Revert "Use serializable exception in GCP listeners (elastic#33657)"
  Adding index refresh (elastic#33647)
  [DOCS] Moves securing-communications to docs (elastic#33640)
  [HLRC][ML] Add ML delete datafeed API to HLRC (elastic#33667)
  Mute testRecoveryWithConcurrentIndexing
  TEST: decrease logging level in the flush test
  DOC: Add SQL section on client applications
  Fix race in global checkpoint listeners test
  Use serializable exception in GCP listeners (elastic#33657)

* master: (24 commits)
  Only notify ready global checkpoint listeners (elastic#33690)
  Don't count hits via the collector if the hit count can be computed from index stats. (elastic#33701)
  Expose retries for CCR fetch failures (elastic#33694)
  Test fix - Graph vertices could appear in different orders based on map insertion sequence (elastic#33709)
  Structured audit logging (elastic#31931)
  Core: Add DateFormatter interface for java time parsing (elastic#33467)
  [CCR] Check whether the rejected execution exception has the shutdown flag set (elastic#33703)
  Mute ClusterDisruptionIT#testSendingShardFailure
  Revert "Mute FullClusterRestartSettingsUpgradeIT"
  Adjust BWC version on settings upgrade test (elastic#33650)
  [ML] Allow overrides for some file structure detection decisions (elastic#33630)
  Adapt skip version for doc_values format deprecation
  [TEST] wait for no initializing shards
  [Docs] Minor fix in `has_child` javadoc comment (elastic#33674)
  Mute FullClusterRestartSettingsUpgradeIT
  [Kerberos] Add realm name & UPN to user metadata (elastic#33338)
  [TESTS] Disable specific locales for RestrictedTrustManagerTest (elastic#33299)
  SQL: Return functions in JDBC driver metadata (elastic#33672)
  SCRIPTING: Move terms_set Context to its Own Class (elastic#33602)
  AwaitsFix testRestoreMinmal
  ...

* master:
  Add script to cache dependencies (elastic#33726)
  [DOCS] Moves security reference to docs folder (elastic#33643)
  Cleanup assertions in global checkpoint listeners (elastic#33722)
  [CCR] Move ccr tests in core module back to ccr module (elastic#33711)
  HLRC: ML PUT Calendar (elastic#33362)
  [Tests] Fix randomization in StringTermsIT (elastic#33678)
  Pin TLS1.2 in SSLConfigurationReloaderTests

* master:
  Move CCR REST tests to a sub-project of ccr
  Move CCR REST tests to ccr sub-project (elastic#33731)
  Move CCR monitoring tests to ccr sub-project (elastic#33730)

* master:
  Do not count shard changes tasks against REST tests (elastic#33738)
  [HLRC][ML] Add ML get datafeed API to HLRC (elastic#33715)