Fixed Allocation Explain API in batch mode

[shiv0408]

Description

This Pull request fixes the explainUnassignedShardAllocation method to use the correct batch allocator to find unassigned explain reason in case the batch mode is enabled.

Related Issues

This is part of improvement for #5098 Related to #8098

Dependency

This change is dependent on #8865, which needs to be merged before merging this PR

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)
• [ ] GitHub issue/PR created in OpenSearch documentation repo for the required public documentation changes (#[Issue/PR number])

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[github-actions[bot]]

Compatibility status:

Checks if related components are compatible with change a730ff5

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[github-actions[bot]]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE :x:
• URL: https://build.ci.opensearch.org/job/gradle-check/26810/
• CommitID: e35add0e10a70d050453e3832796c3a5f3765212 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[bot]]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE :x:
• URL: https://build.ci.opensearch.org/job/gradle-check/28109/
• CommitID: 354a9455dbbee5819ba01c69a20f4e0ce8a6d481 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[bot]]

:x: Gradle check result for a730ff5a460480772a0cd0afc00d82064fa22cdf: 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?

[opensearch-trigger-bot[bot]]

This PR is stalled because it has been open for 30 days with no activity.

[ticheng-aws]

Hi @shiv0408, Is this being worked upon? Feel free to reach out to maintainers for further reviews.

[opensearch-trigger-bot[bot]]

This PR is stalled because it has been open for 30 days with no activity.

[shiv0408]

Discarding this PR as the core logic of explainUnassignedShardAllocation written in this PR is already added in #8746. Will add the test added in this PR to the above mentioned PR only.