[Backport 2.x] [Derived Fields] Add support for emitting multiple values in DerivedFieldScripts

[rishabhmaurya]

Description

Backport from #12837.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

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 c152bfe

Incompatible components

Skipped components

Compatible components

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

[github-actions]

❌ Gradle check result for 6c3ad80: 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 c152bfe: 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 c152bfe: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 80.85106% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 71.30%. Comparing base (0dd892c) to head (c152bfe).
Report is 116 commits behind head on 2.x.

Files	Patch %	Lines
...java/org/opensearch/script/DerivedFieldScript.java	74.19%	7 Missing and 1 partial ⚠️
...n/java/org/opensearch/script/ScriptEmitValues.java	90.90%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #13083      +/-   ##
============================================
+ Coverage     71.28%   71.30%   +0.01%     
- Complexity    60145    60581     +436     
============================================
  Files          4957     4997      +40     
  Lines        282799   284950    +2151     
  Branches      41409    41638     +229     
============================================
+ Hits         201591   203170    +1579     
- Misses        64189    64638     +449     
- Partials      17019    17142     +123     

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