Segment Replication - Update /_cat/segment_replication API with backpressure metrics.

[mch2]

Description

This change updates the existing /_cat/segment_replication API to include backpressure metrics. It does this by returning stats from primary shards for its tracked replication group and merging it with metrics returned from replicas. Primary captured metrics will now appear by default, with replica per sync events showing when detailed=true is set.

Issues Resolved

Resolves #4478

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.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/12463/
• CommitID: a9575f8
  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 (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.persistent.PersistentTasksExecutorFullRestartIT.testFullClusterRestart

• URL: https://build.ci.opensearch.org/job/gradle-check/12464/
• CommitID: cc4218f
  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 #6674 (246362f) into main (1e5d913) will decrease coverage by 0.04%.
The diff coverage is 30.21%.

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@@             Coverage Diff              @@
##               main    #6674      +/-   ##
============================================
- Coverage     70.77%   70.73%   -0.04%     
+ Complexity    59250    59231      -19     
============================================
  Files          4808     4809       +1     
  Lines        283454   283501      +47     
  Branches      40868    40873       +5     
============================================
- Hits         200611   200538      -73     
- Misses        66338    66547     +209     
+ Partials      16505    16416      -89     

Impacted Files	Coverage Δ
...lication/SegmentReplicationShardStatsResponse.java	0.00% <0.00%> (ø)
...earch/index/SegmentReplicationPressureService.java	80.00% <0.00%> (-1.64%)	⬇️
...org/opensearch/index/seqno/ReplicationTracker.java	67.85% <ø> (-0.35%)	⬇️
...cation/TransportSegmentReplicationStatsAction.java	9.80% <3.03%> (-1.01%)	⬇️
...s/replication/SegmentReplicationStatsResponse.java	13.79% <22.22%> (+0.45%)	⬆️
...opensearch/index/SegmentReplicationShardStats.java	36.58% <33.33%> (+4.23%)	⬆️
...st/action/cat/RestCatSegmentReplicationAction.java	45.09% <47.27%> (-5.93%)	⬇️
...nsearch/index/SegmentReplicationPerGroupStats.java	32.00% <60.00%> (+3.42%)	⬆️
.../org/opensearch/index/SegmentReplicationStats.java	15.38% <100.00%> (ø)
...ensearch/index/SegmentReplicationStatsTracker.java	95.45% <100.00%> (+0.21%)	⬆️

... and 485 files with indirect coverage changes

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/12495/
• CommitID: b697a1e

[mch2]

Whitesource scan will be fixed with #6629

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.indices.replication.SegmentReplicationAllocationIT.testSingleIndexShardAllocation
      1 org.opensearch.indices.replication.SegmentReplicationRelocationIT.testFlushAfterRelocation

• URL: https://build.ci.opensearch.org/job/gradle-check/12541/
• CommitID: 246362f
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.indices.replication.SegmentReplicationRelocationIT.testFlushAfterRelocation
      1 org.opensearch.indices.replication.SegmentReplicationAllocationIT.testSingleIndexShardAllocation

• URL: https://build.ci.opensearch.org/job/gradle-check/12540/
• CommitID: 24ebbaa
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-6674-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 188e043585b652676a5fc6d175f81bdca0ce96df
# Push it to GitHub
git push --set-upstream origin backport/backport-6674-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-6674-to-2.x.