[Workload Management] QueryGroup Stats API Logic

[ruai0511]

Description

This change introduces the QueryGroup Stats API as part of this RFC: #12342.

The QueryGroup Stats API schema is:

curl -XGET "localhost:9200/_wlm/stats"

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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 result for f647487: FAILURE

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[github-actions]

❌ Gradle check result for 88c9cff: FAILURE

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[github-actions]

❌ Gradle check result for b66823c: FAILURE

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[github-actions]

❌ Gradle check result for 7dcd545: FAILURE

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[jainankitk]

@ruai0511 - you need to merge from main:

org.opensearch.qa.verify_version_constants.VerifyVersionConstantsIT.testLuceneVersionConstant
Failing for the past 1 build (Since
[#49165](https://build.ci.opensearch.org/job/gradle-check/49165/) )
[Took 0.53 sec.](https://build.ci.opensearch.org/job/gradle-check/49165/testReport/junit/org.opensearch.qa.verify_version_constants/VerifyVersionConstantsIT/testLuceneVersionConstant/history)
Error Message

java.lang.AssertionError: 
Expected: <9.12.0>
     but: was <9.11.1>

[github-actions]

❌ Gradle check result for 7dcd545: 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 75b3da2: FAILURE

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[github-actions]

❌ Gradle check result for 75b3da2: FAILURE

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[github-actions]

❌ Gradle check result for 75b3da2:

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[github-actions]

✅ Gradle check result for 75b3da2: SUCCESS

[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:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-15777-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 b2253f1188c7fb0c5885a221ca160ec6a5ea2259
# Push it to GitHub
git push --set-upstream origin backport/backport-15777-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-15777-to-2.x.