Refactor plugin system index tests to use parameterized test pattern

[llilyy]

Description

• Category
  Refactoring

• Why these changes are required?
  Reviewer feedback suggested adopting the parameterized test suite pattern used in IndexAuthorizationReadOnlyIntTests.java to improve test organization, reduce duplication, and ensure consistent behavior across different cluster configurations.

• What is the old behavior before changes and new behavior after changes?
  Introduced a new PluginSystemIndexIntTests.java class that uses JUnit's Parameterized runner.

Issues Resolved

#5893

Testing

./gradlew :integrationTest --tests "org.opensearch.security.privileges.int_tests.PluginSystemIndexIntTests"
# BUILD SUCCESSFUL

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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.

[nibix]

Thanks a lot for the changes. We have test failures, but I am pretty sure that these will be fixed as soon as #5865 is merged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.69%. Comparing base (70e03b2) to head (31222dd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5895      +/-   ##
==========================================
+ Coverage   73.67%   73.69%   +0.01%     
==========================================
  Files         437      437              
  Lines       26655    26666      +11     
  Branches     3945     3947       +2     
==========================================
+ Hits        19639    19651      +12     
- Misses       5141     5143       +2     
+ Partials     1875     1872       -3     

see 8 files with indirect coverage changes

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[llilyy]

@nibix
I've resolved the conflicts. Could you please review it?

[nibix]

Thank you! 👍

[llilyy]

Hi, @cwperks!
It needs one more approval to proceed. As you've been following this thread, could you please review it?

[cwperks]

@llilyy minor comment on the javadoc, but otherwise lgtm.

[llilyy]

@nibix
The previous approval was removed due to recent code changes. Could you please take another look? Thanks for your help!

[nibix]

Approved ...

I have retriggered one failed CI job, hopefully it will be green soon.