[Workload Management] Add Workload Management Stats IT

[ruai0511]

Add Integration Tests for workload management stats API
For more information regarding workload management, refer to this RFC: #12342.

This IT can be run using

./gradlew :server:internalClusterTest --tests org.opensearch.wlm.WorkloadManagementStatsIT 

[github-actions]

❌ Gradle check result for 867e315: 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 18fe21f: null

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 803ced1: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.03%. Comparing base (691f725) to head (803ced1).
Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
...ain/java/org/opensearch/wlm/QueryGroupService.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16341      +/-   ##
============================================
- Coverage     72.06%   72.03%   -0.03%     
+ Complexity    64822    64787      -35     
============================================
  Files          5308     5308              
  Lines        302574   302558      -16     
  Branches      43710    43709       -1     
============================================
- Hits         218048   217947     -101     
- Misses        66648    66700      +52     
- Partials      17878    17911      +33     

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[github-actions]

❌ Gradle check result for 33aafe5: 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 adb1c1a: 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?