[Backport 2.x] Support scripting for composite aggs in concurrent segment search

[jed326]

Description

Backport #15072

Check List

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

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[jed326]

Might be easier to wait for #15093 to get merged first actually

[github-actions]

❌ Gradle check result for cbf3396: 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 1495aca: 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 9aaf32e: 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 8aa8fcd: SUCCESS

[github-actions]

❕ Gradle check result for 0e04531: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.57%. Comparing base (e03e093) to head (0e04531).

Files	Patch %	Lines
.../bucket/composite/CompositeAggregationFactory.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #15094      +/-   ##
============================================
- Coverage     71.71%   71.57%   -0.14%     
+ Complexity    62868    62755     -113     
============================================
  Files          5125     5125              
  Lines        294586   294588       +2     
  Branches      42934    42934              
============================================
- Hits         211260   210855     -405     
- Misses        65600    66034     +434     
+ Partials      17726    17699      -27     

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[jed326]

@reta could you approve this again? Thanks!