* elastic/master:
  More detailed tracing when writing metadata (elastic#31319)
  [Tests] Mutualize fixtures code in BaseHttpFixture (elastic#31210)
  Remove RestGetAllAliasesAction (elastic#31308)
  Temporary fix for broken build
  Reenable Checkstyle's unused import rule (elastic#31270)
  Remove remaining unused imports before merging elastic#31270
  Fix non-REST doc snippet

* master:
  Remove RestGetAllAliasesAction (#31308)
  Temporary fix for broken build
  Reenable Checkstyle's unused import rule (#31270)
  Remove remaining unused imports before merging #31270
  Fix non-REST doc snippet
  [DOC] Extend SQL docs
  Immediately flush channel after writing to buffer (#31301)
  [DOCS] Shortens ML API intros
  Use quotes in the call invocation (#31249)
  move security ingest processors to a sub ingest directory (#31306)
  Add 5.6.11 version constant.
  Fix version detection.
  SQL: Whitelist SQL utility class for better scripting (#30681)
  [Docs] All Rollup docs experimental, agg limitations, clarify DeleteJob (#31299)
  CCS: don't proxy requests for already connected node (#31273)
  Mute ScriptedMetricAggregatorTests testSelfReferencingAggStateAfterMap
  [test] opensuse packaging turn up debug logging
  Add unreleased version 6.3.1
  Removes experimental tag from scripted_metric aggregation (#31298)
  [Rollup] Metric config parser must use builder so validation runs (#31159)
  [ML] Check licence when datafeeds use cross cluster search  (#31247)
  Add notion of internal index settings (#31286)
  Test: Remove broken yml test feature (#31255)
  REST hl client: cluster health to default to cluster level (#31268)
  [ML] Update test thresholds to account for changes to memory control (#31289)
  Log warnings when cluster state publication failed to some nodes (#31233)
  Fix AntFixture waiting condition (#31272)
  Ignore numeric shard count if waiting for ALL (#31265)
  [ML] Implement new rules design (#31110)
  index_prefixes back-compat should test 6.3 (#30951)
  Core: Remove plain execute method on TransportAction (#30998)
  Update checkstyle to 8.10.1 (#31269)
  Set analyzer version in PreBuiltAnalyzerProviderFactory (#31202)
  Modify pipelining handlers to require full requests (#31280)
  Revert upgrade to Netty 4.1.25.Final (#31282)
  Use armored input stream for reading public key (#31229)
  Fix Netty 4 Server Transport tests. Again.
  REST hl client: adjust wait_for_active_shards param in cluster health (#31266)
  REST high-level Client: remove deprecated API methods (#31200)
  [DOCS] Mark SQL feature as experimental
  [DOCS] Updates machine learning custom URL screenshots (#31222)
  Fix naming conventions check for XPackTestCase
  Fix security Netty 4 transport tests
  Fix race in clear scroll (#31259)
  [DOCS] Clarify audit index settings when remote indexing (#30923)
  Delete typos in SAML docs (#31199)
  REST high-level client: add Cluster Health API (#29331)
  [ML][TEST] Mute tests using rules (#31204)
  Support RequestedAuthnContext (#31238)
  SyncedFlushResponse to implement ToXContentObject (#31155)
  Add Get Aliases API to the high-level REST client (#28799)
  Remove some line length supressions (#31209)
  Validate xContentType in PutWatchRequest. (#31088)
  [INGEST] Interrupt the current thread if evaluation grok expressions take too long (#31024)
  Suppress extras FS on caching directory tests
  Revert "[DOCS] Added 6.3 info & updated the upgrade table. (#30940)"
  Revert "Fix snippets in upgrade docs"
  Fix snippets in upgrade docs
  [DOCS] Added 6.3 info & updated the upgrade table. (#30940)
  LLClient: Support host selection (#30523)
  Upgrade to Netty 4.1.25.Final (#31232)
  Enable custom credentials for core REST tests (#31235)
  Move ESIndexLevelReplicationTestCase to test framework (#31243)
  Encapsulate Translog in Engine (#31220)
  HLRest: Add get index templates API (#31161)
  Remove all unused imports and fix CRLF (#31207)
  [Tests] Fix self-referencing tests
  [TEST] Fix testRecoveryAfterPrimaryPromotion
  [Docs] Remove mention pattern files in Grok processor (#31170)
  Use stronger write-once semantics for Azure repository (#30437)
  Don't swallow exceptions on replication (#31179)
  Limit the number of concurrent requests per node (#31206)
  Call ensureNoSelfReferences() on _agg state variable after scripted metric agg script executions (#31044)
  Move java version checker back to its own jar (#30708)
  [test] add fix for rare virtualbox error (#31212)

We currently have a specific REST action to retrieve all aliaes, which
uses internally the get index API. This doesn't seem to be required
anymore though as the existing RestGetAliaesAction could as well take
the requests with no indices and aliases specified.

This commit removes the RestGetAllAliasesAction in favour of using
RestGetAliasesAction also for requests that don't specify indices nor
aliases. Similar to #31129.

* 6.x:
  Upgrade to Lucene-7.4.0-snapshot-518d303506 (#31360)
  [ML] Implement new rules design (#31110) (#31294)
  Remove RestGetAllAliasesAction (#31308)
  CCS: don't proxy requests for already connected node (#31273)
  Rankeval: Fold template test project into main module (#31203)
  [Docs] Remove reference to repository-s3 plugin creating an S3 bucket (#31359)
  More detailed tracing when writing metadata (#31319)
  Add details section for dcg ranking metric (#31177)

Some recent failures on the mixed cluster tests were caused by elastic#31308.
Instead of executing get index API when calling GET /_alias we now go
through the get alias API. The behaviour of such API is slightly
different on 5.6 compared to 6.x and master as to whether indices that
have no aliases are returned or not. In fact elastic#25114 was not backported
to 5.6.

When the 5.6 node is the elected master, if the get alias API goes
through such node or another 5.x node, the get index API will be used
internally and all tests are fine. If some 6.x node is hit though by the
client request, we will go through the get alias API, but we will do it
through the elected master which will not return indices without aliases
(at transport, see MetaData#findAliases on 5.6). That means that in a
mixed cluster this API will return a different result depending on which
node is the elected master and which one is hit by the request.

Some recent failures on the mixed cluster tests were caused by #31308.
Instead of executing get index API when calling GET /_alias we now go
through the get alias API. The behaviour of such API is slightly
different on 5.6 compared to 6.x and master as to whether indices that
have no aliases are returned or not. In fact #25114 was not backported
to 5.6.

When the 5.6 node is the elected master, if the get alias API goes
through such node or another 5.x node, the get index API will be used
internally and all tests are fine. If some 6.x node is hit though by the
client request, we will go through the get alias API, but we will do it
through the elected master which will not return indices without aliases
(at transport, see MetaData#findAliases on 5.6). That means that in a
mixed cluster this API will return a different result depending on which
node is the elected master and which one is hit by the request.

This reverts commit 38b1a5f.

Relates to #31516

* 6.x:
  Fix broken backport of #31578 by adjusting constructor (#31587)
  ingest: Add ignore_missing property to foreach filter (#22147) (#31578)
  Add package pre-install check for java binary (#31343)
  Docs: Clarify sensitive fields watcher encryption (#31551)
  Watcher: Remove never executed code (#31135)
  Improve test times for tests using `RandomObjects::addFields` (#31556)
  Revert "Remove RestGetAllAliasesAction (#31308)"
  REST high-level client: add simulate pipeline API (#31158)
  Get Mapping API to honour allow_no_indices and ignore_unavailable (#31507)
  Fix Mockito trying to mock IOException that isn't thrown by method (#31433) (#31527)
  [Test] Add full cluster restart test for Rollup (#31533)
  Enhance thread context uniqueness assertion
  fix writeIndex evaluation for aliases (#31562)
  Add x-opaque-id to search slow logs (#31539)
  Watcher: Fix put watch action (#31524)
  [DOCS] Significantly improve SQL docs
  turn GetFieldMappingsResponse to ToXContentObject (#31544)
  TEST: Unmute testHistoryUUIDIsGenerated
  Ingest Attachment: Upgrade Tika to 1.18 (#31252)
  TEST: Correct the assertion arguments order (#31540)