Fix: Revert unintended bulk sink changes that broke test case search indexing

[sonika-shah]

Summary

• Restores 6 files to their pre-2839bc259f state, removing unintended changes from PR #27153 that were cherry-picked to 1.12.5 alongside the revert of PR #27103
• PR Set Indexing related executor threads priority to LOW  #27153 ("Improve memory usage for reindex") is still open/unmerged on main — these changes were never meant for 1.12.5

Problem

Commit 2839bc259f changed the bulk sink serialization path from:

// Before (correct — matches main)
String json = JsonUtils.pojoToJson(searchIndexDoc);
document(EsUtils.toJsonData(json));  // Date → ISO string via Jackson

to:

// After (broken — from PR #27153)
JsonData jsonData = EsUtils.toJsonData(searchIndexDoc);  // Date → epoch Long, bypasses Jackson
document(jsonData);

This caused java.util.Date fields (like tags.appliedAt) to be sent as raw epoch Long during reindex. OpenSearch dynamically mapped tags.appliedAt as long. Later, real-time indexing sent appliedAt as ISO string → mapper_parsing_exception:

failed to parse field [tags.appliedAt] of type [long]
Preview of field's value: '2026-04-09T01:51:10.000160Z'

Test cases with tags were created in DB but silently never indexed in search, causing DataQuality.spec.ts > TestCase filters to fail.

Files restored

File	What was reverted
ElasticSearchBulkSink.java	Back to pojoToJson → string → toJsonData(string)
OpenSearchBulkSink.java	Same
EsUtils.java	Removed toJsonData(Object) overload
OsUtils.java	Same
SearchIndexExecutor.java	Removed contextDataCache, Thread.MIN_PRIORITY
ReindexingMetrics.java	Removed counter caching

Test plan

• Reindex after deployment to recreate indices with correct dynamic mappings
• Run DataQuality.spec.ts > TestCase filters — should pass
• Verify no mapper_parsing_exception errors in server logs for tags.appliedAt
• Verify test cases with tags appear in search results after creation

[gitar-bot]

Code Review ✅ Approved

Reverts unintended bulk sink changes that were breaking test case search indexing. No issues found.

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