Add Flint Index Purging Logic

[kaituo]

Description

• Introduce dynamic settings for enabling/disabling purging and controlling index TTL.
• Reuse default result index name as a common prefix for all result indices.
• Change result index to a non-hidden index for better user experience.
• Allow custom result index specification in the data source.
• Move default result index name from spark to core package to avoid cross-package references.
• Add validation for provided result index name in the data source.
• Use pattern prefix + data source name for default result index naming.

Testing:

• Verified old documents are purged in a cluster setup.
• Checked result index naming with and without custom names, ensuring validation is applied.

Note: Tests will be added in a subsequent PR.

Issues Resolved

#2331

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• 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.

[codecov]

Codecov Report

Merging #2378 (1ee8c03) into main (e16da37) will increase coverage by 0.57%.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #2378      +/-   ##
============================================
+ Coverage     96.46%   97.04%   +0.57%     
+ Complexity     4918     4538     -380     
============================================
  Files           465      401      -64     
  Lines         13521    11806    -1715     
  Branches        913      792     -121     
============================================
- Hits          13043    11457    -1586     
+ Misses          458      343     -115     
+ Partials         20        6      -14     

Flag	Coverage Δ
sql-engine	97.04% <100.00%> (+0.57%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...rch/sql/opensearch/setting/OpenSearchSettings.java	100.00% <100.00%> (ø)

... and 64 files with indirect coverage changes