[Backport 2.x] [Remote Store] Fix stats api bugs (#7739) & (#7774)

[ashking94]

Description

This backports #7739 & #7775

Related Issues

Resolves #7738 & #7774

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/16577/
• CommitID: b33557d
  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: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/16578/
• CommitID: 7bf177c
  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: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/16586/
• CommitID: 104d9a0

[codecov]

Codecov Report

Merging #7838 (104d9a0) into 2.x (050d418) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                2.x    #7838      +/-   ##
============================================
- Coverage     70.66%   70.57%   -0.10%     
+ Complexity    56437    56426      -11     
============================================
  Files          4665     4665              
  Lines        267672   267674       +2     
  Branches      39634    39634              
============================================
- Hits         189154   188901     -253     
- Misses        62216    62502     +286     
+ Partials      16302    16271      -31     

Impacted Files	Coverage Δ
...testore/stats/TransportRemoteStoreStatsAction.java	45.94% <100.00%> (+4.27%)	⬆️
...arch/index/remote/RemoteRefreshSegmentTracker.java	88.54% <100.00%> (+0.05%)	⬆️

... and 457 files with indirect coverage changes