[Segment Replication] Make SegmentReplicationPressureService a Singleton class and fix bug of rejected_requests reporting incorrect value

[Rishikesh1159]

Description

This PR makes SegmentReplicationPressureService a Singleton class. This way we will only have one instance of SegmentReplicationPressureService per node.

This PR will resolve the bug of rejected_requests column not getting updated in _cat/segment_replication API.

Problem:

-> Initially we were having two instances of SegmentReplicationPressureService. One intstance being used by backpressure mechanism and another instance being used by SegmentReplicationStatsAction class (used by _cat/segment_replication API).

-> As we were having two instances of SegmentReplicationStatsAction class, the changes made by backpressure mechanism are not updated to another instance, so the value of rejected_requests is always being 0 and never getting updated.

Solution:

-> The solution here would be to make SegmentReplicationStatsAction class a singleton class so that there is only one instance of SegmentReplicationStatsAction class per node and value of rejected_requests is always updated correctly.

Issues Resolved

#7275

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: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/14431/
• CommitID: aa2714c

[codecov-commenter]

Codecov Report

Merging #7274 (aa2714c) into main (0763d02) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

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@@             Coverage Diff              @@
##               main    #7274      +/-   ##
============================================
- Coverage     70.72%   70.65%   -0.08%     
+ Complexity    59568    59531      -37     
============================================
  Files          4862     4862              
  Lines        285530   285531       +1     
  Branches      41153    41153              
============================================
- Hits         201936   201729     -207     
- Misses        66980    67170     +190     
- Partials      16614    16632      +18     

Impacted Files	Coverage Δ
...ain/java/org/opensearch/indices/IndicesModule.java	98.19% <100.00%> (+0.01%)	⬆️

... and 467 files with indirect coverage changes

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