[Backport 2.x] Change INDEX_SEARCHER threadpool to auto queue to support task resource tracking

[jed326]

Description

Backports #7502

Concurrent segment search has been backported to 2.x so we also need to backport #7502 so that we are not missing out on resource tracking whenever concurrent search is GA.

Since Resizable threadpool type does not exist in 2.x, we will use the same auto queue threadpool type that search threadpool uses in 2.x.

Ref #7613

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)

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Resolves #7743

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/16326/
• CommitID: 3f0848d
  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 (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/16327/
• CommitID: 484565d
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[jed326]

@reta this is the backport for #7502 which you previously helped approved. Could you please take a look? Thanks!

[codecov]

Codecov Report

Merging #7765 (484565d) into 2.x (bb10bdf) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##                2.x    #7765      +/-   ##
============================================
- Coverage     70.56%   70.53%   -0.03%     
+ Complexity    56409    56372      -37     
============================================
  Files          4665     4665              
  Lines        267683   267683              
  Branches      39638    39638              
============================================
- Hits         188885   188810      -75     
- Misses        62512    62607      +95     
+ Partials      16286    16266      -20     

Impacted Files	Coverage Δ
...ain/java/org/opensearch/threadpool/ThreadPool.java	83.09% <0.00%> (-0.88%)	⬇️

... and 449 files with indirect coverage changes

[jed326]

Flaky test looks like #6761