feat(search): unified entity index

[david-leifker]

Introduce a new unified entity index which consolidates entity indices (100+) into a few indices. It will eventually also replace the system metadata index. This is disabled by default and only contains code for the write path at this time.

Major Features

• Unified Search Indexes: Partial implementation supporting v3 entity index management, settings/mappings, and dual writes (current v2 & v3)
• Search Index Groups: New entity registry configuration for managing multiple search index entity groups

Key Components Added

• MultiEntityMappingsBuilder - Unified mapping generation
• UpdateIndicesV2Strategy & UpdateIndicesV3Strategy - Index update strategies
• SearchableAnnotationValidator - Validation for search annotations
• DelegatingMappingsBuilder & DelegatingSettingsBuilder - Delegation patterns

Configuration Changes

• New entity registry YAML configuration for search index groups

[codecov]

Codecov Report

❌ Patch coverage is 78.29109% with 531 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ch/index/entity/v3/MultiEntityMappingsBuilder.java	77.29%	69 Missing and 25 partials ⚠️
...edin/metadata/service/UpdateIndicesV2Strategy.java	65.62%	57 Missing and 9 partials ⚠️
...elasticsearch/index/entity/v3/FieldTypeMapper.java	59.55%	29 Missing and 7 partials ⚠️
...rch/elasticsearch/indexbuilder/ESIndexBuilder.java	63.15%	22 Missing and 6 partials ⚠️
...elasticsearch/index/DelegatingMappingsBuilder.java	82.87%	19 Missing and 6 partials ⚠️
...elasticsearch/index/DelegatingSettingsBuilder.java	53.06%	22 Missing and 1 partial ⚠️
...inkedin/metadata/service/UpdateIndicesService.java	67.69%	15 Missing and 6 partials ⚠️
...lasticsearch/index/entity/v3/ConflictResolver.java	79.59%	13 Missing and 7 partials ⚠️
...tadata/search/elasticsearch/update/ESWriteDAO.java	31.03%	20 Missing ⚠️
...ata/search/elasticsearch/ElasticSearchService.java	15.78%	16 Missing ⚠️
... and 31 more

📢 Thoughts on this report? Let us know!

[alwaysmeticulous]

✅ Meticulous spotted 0 visual differences across 993 screens tested: view results.

Meticulous evaluated ~8 hours of user flows against your PR.

_{Expected differences? Click here. Last updated for commit d937d9e. This comment will update as new commits are pushed.}

[codecov]

Bundle Report

Bundle size has no change ✅

[abedatahub]

Approving.

I flagged a couple of tests for over-testing. There must be others but I haven't looked.

I think #15073 has proved its usefulness (the guidelines are good but I haven't verified that claude code does the right thing when generating new unit tests).