Add read and write optional enum sets methods to stream input and output

[q-andy]

Description

In some plugins there are use cases to read and write optional EnumSets to and from StreamOutput/StreamInput, similar to existing readOptionalStringCollection/writeOptionalStringList methods.

Currently this is done with plugin specific private helper methods, but since this functionality is common to multiple plugins and we are planning on building similar systems for geospatial and search relevance lab plugins, it may be more elegant to consolidate them in core. Examples:

• ml-commons MLStatsInput
• Open PR for neural search NeuralStatsInput

Related Issues

n/a

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for ad0c5ce: FAILURE

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❌ Gradle check result for 52f24d4: FAILURE

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[q-andy]

@dbwiddis thanks for the review, I added unit tests to the BaseStreamTests in core so all the StreamInput implementations should inherit tests as well

[github-actions]

❌ Gradle check result for f65cfc8: FAILURE

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❌ Gradle check result for 9ff9553: FAILURE

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[dbwiddis]

LGTM pending changelog

[dbwiddis]

DCO failing, looks like no email address:

Commit sha: 78de87a, Author: Andy Qin, Committer: Andy Qin; The sign-off is missing.

[github-actions]

❕ Gradle check result for 78de87a: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.snapshots.DedicatedClusterSnapshotRestoreIT.testSnapshotWithStuckNode

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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.38%. Comparing base (2ee8660) to head (221f397).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17556      +/-   ##
============================================
- Coverage     72.43%   72.38%   -0.05%     
- Complexity    65694    65719      +25     
============================================
  Files          5311     5311              
  Lines        304937   304945       +8     
  Branches      44226    44226              
============================================
- Hits         220872   220745     -127     
- Misses        65912    66061     +149     
+ Partials      18153    18139      -14     

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[github-actions]

❌ Gradle check result for 221f397: FAILURE

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?

[github-actions]

❕ Gradle check result for 221f397: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.snapshots.DedicatedClusterSnapshotRestoreIT.testSnapshotWithStuckNode

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.