Today when a flush is performed, the translog is committed and if there
are no outstanding views, only the current translog generation is
preserved. Yet for the purpose of sequence numbers, we need stronger
guarantees than this. This commit migrates the preservation of translog
generations to keep the minimum generation that would be needed to
recover after the local checkpoint.

* master: (41 commits)
  Remove awaits fix from evil JNA native tests
  Correct handling of default and array settings
  Build: Switch jna dependency to an elastic version (elastic#24081)
  fix CategoryContextMappingTests compilation bugs
  testConcurrentGetAndSetOnPrimary - fix a race condition between indexing and updating value map
  Allow different data types for category in Context suggester (elastic#23491)
  Restrict build info loading to ES jar, not any jar (elastic#24049)
  Remove more hidden file leniency from plugins
  Register error listener in evil logger tests
  Detect using logging before configuration
  [DOCS] Added note about Elastic Cloud to improve 'elastic aws' SERP results.
  Add version constant for 5.5 (elastic#24075)
  Add unit tests for NestedAggregator (elastic#24054)
  Add more debugging information to rethrottles
  Tests: Use random analyzer only on string fields in Match/MultiMatchBuilderTests
  Cleanup outdated comments for fixing up pom dependencies (elastic#24056)
  S3 Repository: Eagerly load static settings (elastic#23910)
  Reject duplicate settings on the command line
  Wildcard cluster names for cross cluster search (elastic#23985)
  Update scripts/security docs for sandboxed world (elastic#23977)
  ...