This commit adds tracking and reporting for fetch exceptions. We track
fetch exceptions per fetch, keeping track of up to the maximum number of
concurrent fetches. With each failing fetch, we associate the from
sequence number with the exception that caused the fetch. We report
these in the CCR stats endpoint, and add some testing for this tracking.

* ccr: (71 commits)
  Make CCR QA tests build again (elastic#33113)
  Add hook to skip asserting x-content equivalence (elastic#33114)
  Muted testListenersThrowingExceptionsDoNotCauseOtherListenersToBeSkipped
  [Rollup] Move getMetadata() methods out of rollup config objects (elastic#32579)
  fixed not returning response instance
  Muted testEmptyAuthorizedIndicesSearchForAllDisallowNoIndices
  Update Google Cloud Storage Library for Java (elastic#32940)
  Remove unsupported Version.V_5_* (elastic#32937)
  Required changes after merging in master branch.
  [DOCS] Add docs for Application Privileges (elastic#32635)
  Add versions 5.6.12 and 6.4.1
  Do NOT allow termvectors on nested fields (elastic#32728)
  [Rollup] Return empty response when aggs are missing (elastic#32796)
  [TEST] Add some ACL yaml tests for Rollup (elastic#33035)
  Move non duplicated actions back into xpack core (elastic#32952)
  Test fix - GraphExploreResponseTests should not randomise array elements Closes elastic#33086
  Use `addIfAbsent` instead of checking if an element is contained
  TESTS: Fix Random Fail in MockTcpTransportTests (elastic#33061)
  HLRC: Fix Compile Error From Missing Throws (elastic#33083)
  [DOCS] Remove reload password from docs cf. elastic#32889
  ...