[Backport 2.x] feat: constant keyword field

[msfroh]

Constant keyword fields behave similarly to regular keyword fields, except that they are defined only in the index mapping, and all documents in the index appear to have the same value for the constant keyword field.

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Signed-off-by: Mohammad Hasnain hasnain2808@gmail.com
(cherry picked from commit 1ec49bd)

Manual backport for #12285

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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[github-actions]

Compatibility status:

Checks if related components are compatible with change b30e877

Incompatible components

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/flow-framework.git, https://github.com/opensearch-project/observability.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/k-nn.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/performance-analyzer.git]

[github-actions]

❌ Gradle check result for 2ef020e: 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 2ef020e: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 74.41860% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 71.28%. Comparing base (0dd892c) to head (b30e877).
Report is 138 commits behind head on 2.x.

Files	Patch %	Lines
...earch/index/mapper/ConstantKeywordFieldMapper.java	73.80%	8 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##                2.x   #13003     +/-   ##
===========================================
  Coverage     71.28%   71.28%             
- Complexity    60145    60701    +556     
===========================================
  Files          4957     5004     +47     
  Lines        282799   285376   +2577     
  Branches      41409    41724    +315     
===========================================
+ Hits         201591   203432   +1841     
- Misses        64189    64763    +574     
- Partials      17019    17181    +162     

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[github-actions]

✅ Gradle check result for b30e877: SUCCESS