[Backport 2.x] Cleanup interfaces around ExtensionManager (#7374)

[peternied]

Description

ExtensionsManager has a whole lot of functionality that shouldn't be exposed to external classes, marked much of this package protected for a cleaner interface. Then updated the Noop version to override all public functions to remove extraneous feature flag checks.

Note; I didn't go so far to remove all getters/setters that were unused but that could be a good follow up in the future.

Signed-off-by: Peter Nied [email protected]
(cherry picked from commit 3687d01)

Related Issues

• Related Cleanup interfaces around ExtensionManager #7374

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[peternied]

FYI @cwperks Once this is merged and built it will unblock opensearch-project/security#2743

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/14956/
• CommitID: 4eb2148
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[peternied]

Same test failed 4 times, looks unrelated, to this change, but could be a break on the 2.x line

org.opensearch.search.aggregations.bucket.terms.SignificantTextAggregatorTests.testSupportedFieldTypes

Error Details
java.lang.AssertionError: Aggregator [significant_text] supports field type [unsigned_long] but executing against the field threw an exception: [Value [0] is out of range for an unsigned long]

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/15092/
• CommitID: 4eb2148
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov-commenter]

Codecov Report

Merging #7451 (4eb2148) into 2.x (708b28c) will increase coverage by 0.15%.
The diff coverage is 60.60%.

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@@             Coverage Diff              @@
##                2.x    #7451      +/-   ##
============================================
+ Coverage     70.11%   70.26%   +0.15%     
- Complexity    59775    59849      +74     
============================================
  Files          4873     4873              
  Lines        288130   288053      -77     
  Branches      41885    41879       -6     
============================================
+ Hits         202018   202401     +383     
+ Misses        69168    68711     -457     
+ Partials      16944    16941       -3     

Impacted Files	Coverage Δ
...a/org/opensearch/extensions/ExtensionsManager.java	45.34% <18.18%> (+1.94%)	⬆️
...g/opensearch/extensions/NoopExtensionsManager.java	66.66% <66.66%> (-33.34%)	⬇️
server/src/main/java/org/opensearch/node/Node.java	86.58% <91.66%> (+1.74%)	⬆️
...in/java/org/opensearch/indices/IndicesService.java	68.92% <100.00%> (+4.86%)	⬆️

... and 489 files with indirect coverage changes