[Backport 2.12] Increase index_searcher thread count to 2x processor (#12196)

[jed326]

Description

Backport #12196 to 2.12

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[jed326]

@reta @sohami @kotwanikunal Here is the backport to 2.12 for #12196

[github-actions]

Compatibility status:

Checks if related components are compatible with change e3fe7f3

Incompatible components

Incompatible components: [https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/performance-analyzer.git]

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/neural-search.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/flow-framework.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/alerting.git]

[github-actions]

✅ Gradle check result for e3fe7f3: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (2.12@1cc61a4). Click here to learn what that means.

Additional details and impacted files

@@           Coverage Diff           @@
##             2.12   #12207   +/-   ##
=======================================
  Coverage        ?   71.08%           
  Complexity      ?    59758           
=======================================
  Files           ?     4929           
  Lines           ?   281350           
  Branches        ?    41202           
=======================================
  Hits            ?   200009           
  Misses          ?    64426           
  Partials        ?    16915           

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