* master: (278 commits)
  Move pre-6.0 node checkpoint to SequenceNumbers
  Invalid JSON request body caused endless loop (elastic#26680)
  added comment
  fix line length violation
  Moved the check to fetch phase. This basically means that we throw a better error message instead of an AOBE and not adding more restrictions.
  inner hits: Do not allow inner hits that use _source and have a non nested object field as parent
  Separate Painless Whitelist Loading from the Painless Definition (elastic#26540)
  convert more admin requests to writeable (elastic#26566)
  Handle release of 5.6.1
  Allow `InputStreamStreamInput` array size validation where applicable (elastic#26692)
  Update global checkpoint with permit after recovery
  Filter pre-6.0 nodes for checkpoint invariants
  Skip bad request REST test on pre-6.0
  Reenable BWC tests after disabling for backport
  Add global checkpoint tracking on the primary
  [Test] Fix reference/cat/allocation/line_8 test failure
  [Docs] improved description for fs.total.available_in_bytes (elastic#26657)
  Fix discovery-file plugin to use custom config path
  fix testSniffNodes to use the new error message
  Add check for invalid index in WildcardExpressionResolver (elastic#26409)
  ...

* master: (67 commits)
  Restoring from snapshot should force generation of a new history uuid (elastic#26694)
  test: Use a single primary shard so that the exception can caught in the same way
  Move pre-6.0 node checkpoint to SequenceNumbers
  Invalid JSON request body caused endless loop (elastic#26680)
  added comment
  fix line length violation
  Moved the check to fetch phase. This basically means that we throw a better error message instead of an AOBE and not adding more restrictions.
  inner hits: Do not allow inner hits that use _source and have a non nested object field as parent
  Separate Painless Whitelist Loading from the Painless Definition (elastic#26540)
  convert more admin requests to writeable (elastic#26566)
  Handle release of 5.6.1
  Allow `InputStreamStreamInput` array size validation where applicable (elastic#26692)
  Update global checkpoint with permit after recovery
  Filter pre-6.0 nodes for checkpoint invariants
  Skip bad request REST test on pre-6.0
  Reenable BWC tests after disabling for backport
  Add global checkpoint tracking on the primary
  [Test] Fix reference/cat/allocation/line_8 test failure
  [Docs] improved description for fs.total.available_in_bytes (elastic#26657)
  Fix discovery-file plugin to use custom config path
  ...