[Backport 2.x] add query group stats constructs

[opensearch-trigger-bot]

Backport c0bcacb from #15343.

[github-actions]

✅ Gradle check result for 7e8212d: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 89.18919% with 12 lines in your changes missing coverage. Please review.

Project coverage is 71.65%. Comparing base (635d2e9) to head (7e8212d).
Report is 3 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...java/org/opensearch/wlm/stats/QueryGroupStats.java	87.20%	4 Missing and 7 partials ⚠️
...java/org/opensearch/wlm/stats/QueryGroupState.java	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #15473      +/-   ##
============================================
- Coverage     71.72%   71.65%   -0.08%     
+ Complexity    63647    63615      -32     
============================================
  Files          5214     5216       +2     
  Lines        297407   297515     +108     
  Branches      43290    43302      +12     
============================================
- Hits         213312   213180     -132     
- Misses        66303    66515     +212     
- Partials      17792    17820      +28     

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[reta]

@jainankitk why we are merging pull request with breaking checks?

[jainankitk]

@jainankitk why we are merging pull request with breaking checks?

@reta Ah, my bad! Missed the breaking check. Any reason the check is not required?

[reta]

@jainankitk why we are merging pull request with breaking checks?

@reta Ah, my bad! Missed the breaking check. Any reason the check is not required?

I think we have difficulties configuring different checks for different branches, it is present in 2.x only but not 3.x

[jainankitk]

@jainankitk why we are merging pull request with breaking checks?

@reta Ah, my bad! Missed the breaking check. Any reason the check is not required?

I think we have difficulties configuring different checks for different branches, it is present in 2.x only but not 3.x

Got it! Let us see how we can improve this as part of #15484

[kaushalmahi12]

@reta How does the backward compatibility plugin works ? Because as per my understanding, if a node in source version cluster is moving an object to a node in target OS version then all it is doing is sending a binary representation of a string which the target node already has source code to decode and initialise the new object (just under different package).

I ran the gradle task locally and following is erroneous abstract

[kaushalmahi12]

I think this is java serialisation issue not the OS level serialisation. Now since the enum has moved from one package to another the java serialisation will break but is that even necessary in this case @reta @jainankitk
?