Implement parallel execution of sub-queries for hybrid search

[VijayanB]

Description

1. Add new thread pool to schedule tasks that are related to hybrid query execution
2. Register executor builders with Plugin
3. Use Lucene's Task Executor to execute and collect results
4. Parallelize Query re-write
5. Parallelize score supplier creation
6. Parallelize build hybrid scores

Issues Resolved

#279

Check List

• [x] New functionality includes testing.
  • [x] All tests pass
• [ ] New functionality has been documented.
  • [ ] New functionality has javadoc added
• [x] Commits are signed as per the DCO using --signoff

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.78378% with 12 lines in your changes are missing coverage. Please review.

Please upload report for BASE (feature/parallelize-hybrid-search@806042c). Learn more about missing BASE report.

:exclamation: Current head 2750ad4 differs from pull request most recent head bc6b885

Please upload reports for the commit bc6b885 to get more accurate results.

Files	Patch %	Lines
...ch/neuralsearch/executors/HybridQueryExecutor.java	44.44%	4 Missing and 1 partial :warning:
...org/opensearch/neuralsearch/query/HybridQuery.java	89.47%	2 Missing :warning:
...ensearch/neuralsearch/query/HybridQueryScorer.java	86.66%	2 Missing :warning:
...ensearch/neuralsearch/query/HybridQueryWeight.java	85.71%	2 Missing :warning:
...g/opensearch/neuralsearch/plugin/NeuralSearch.java	50.00%	1 Missing :warning:

Additional details and impacted files

@@                         Coverage Diff                          @@
##             feature/parallelize-hybrid-search     #749   +/-   ##
====================================================================
  Coverage                                     ?   84.89%           
  Complexity                                   ?      812           
====================================================================
  Files                                        ?       65           
  Lines                                        ?     2490           
  Branches                                     ?      410           
====================================================================
  Hits                                         ?     2114           
  Misses                                       ?      213           
  Partials                                     ?      163           

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[VijayanB]

@navneet1v Can you take a look at one more time? Thanks

[vibrantvarun]

@VijayanB I will reviewing the PR today in sometime.