Add tracking for long running SearchTask post cancellation

[ruai0511]

Description

This PR addes tracking logic for SearchTask to monitor rogue queries at the coordinator level. Previously, the service only tracked SearchShardTask (queries at the shard level) that were cancelled but continued running.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]
#17719

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 ea4d4da:

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 c940580: 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 5d0ecd3: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 74.41860% with 11 lines in your changes missing coverage. Please review.

Project coverage is 72.32%. Comparing base (5f1b4ab) to head (5d0ecd3).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
...va/org/opensearch/tasks/TaskCancellationStats.java	50.00%	2 Missing and 4 partials ⚠️
...nsearch/tasks/BaseSearchTaskCancellationStats.java	77.27%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main   #17726   +/-   ##
=========================================
  Coverage     72.32%   72.32%           
+ Complexity    66005    65969   -36     
=========================================
  Files          5356     5360    +4     
  Lines        306446   306504   +58     
  Branches      44395    44405   +10     
=========================================
+ Hits         221634   221685   +51     
- Misses        66660    66671   +11     
+ Partials      18152    18148    -4     

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[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-17726-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 e9d8e0007b58f96a89b1a400a14eb2ed9f7aa597
# Push it to GitHub
git push --set-upstream origin backport/backport-17726-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-17726-to-2.x.