Merge branch 'master' into get-aliases-not-found

* master:
  Add support for clear scroll to high level REST client (#25038)
  Tiny correction in inner-hits.asciidoc (#25066)
  Added release notes for 6.0.0-alpha2
  Expand index expressions against indices only when managing aliases (#23997)
  Collapse inner hits rest test should not skip 5.x
  Settings: Fix secure settings by prefix (#25064)
  add `exclude_keys` option to KeyValueProcessor (#24876)
  Test: update missing body tests to run against versions >= 5.5.0
  Track EWMA[1] of task execution time in search threadpool executor
  Removes an invalid assert in resizing big arrays which does not always hold (resizing can result in a smaller size than the current size, while the assert attempted to verify the new size is always greater than the current).
  Fixed NPEs caused by requests without content. (#23497)
  Plugins can register pre-configured char filters (#25000)
  Build: Allow preserving shared dir (#24962)
  Tests: Make secure settings available from settings builder for tests (#25037)