Optimising _cat/allocation API to use index level stats

[gargharsh3134]

Description

This PR involves changes, to onboard _cat/allocation API to use index level stats.

Related Issues

Related to #13340

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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 a14c91b: 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 e091736: 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 5901491: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.97%. Comparing base (729e40d) to head (b1ff7ae).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
...ensearch/rest/action/cat/RestAllocationAction.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #15292      +/-   ##
============================================
+ Coverage     71.95%   71.97%   +0.01%     
- Complexity    64192    64227      +35     
============================================
  Files          5270     5271       +1     
  Lines        300052   300167     +115     
  Branches      43368    43380      +12     
============================================
+ Hits         215917   216041     +124     
+ Misses        66442    66415      -27     
- Partials      17693    17711      +18     

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[github-actions]

❌ Gradle check result for 5697580: 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 52b44fe: 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 52b44fe: 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 b1ff7ae: 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-15292-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 6f2ea3928f8af116fdbf023828681bbd02911ef6
# Push it to GitHub
git push --set-upstream origin backport/backport-15292-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-15292-to-2.x.

[opensearch-trigger-bot]

The backport to 2.17 failed:

The process '/usr/bin/git' failed with exit code 1

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-2.17 2.17
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.17
# Create a new branch
git switch --create backport/backport-15292-to-2.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 6f2ea3928f8af116fdbf023828681bbd02911ef6
# Push it to GitHub
git push --set-upstream origin backport/backport-15292-to-2.17
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.17

Then, create a pull request where the base branch is 2.17 and the compare/head branch is backport/backport-15292-to-2.17.