Implement proper casing for Explore quick filters using sourceFields

[owlbotgit]

Problem

Explore quick filters are currently displaying values in lowercase for entity types, domains, owners, and other aggregation-based filters. This creates a poor user experience as the proper casing is not preserved.

Solution

Backend support is already available via the aggregate API's sourceFields parameter (implemented in #20734). This adds a top_hits sub-aggregation that returns original-cased values from _source.

The Advanced Search query builder already uses this pattern successfully - see AdvancedSearchClassBase.ts:821 where it passes sourceFields: 'name' and parseBucketsData in SearchUtils.tsx:346 reads the original case from top_hits#top.

Implementation Steps

1. For entity types: Handle on UI side directly (can be done without backend changes)
2. For domains, owners, and other filters:
   • In ExploreQuickFilters.tsx, when calling getAggregationOptions (~line 118), pass sourceFields for the field being queried:
     • "domains.displayName" for domains
     • "owners.displayName" for owners
     • Similar patterns for other fields
   • In getOptionsFromAggregationBucket (AdvancedSearchUtils.tsx:371), instead of using bucket.key as the label, read the original value from bucket['top_hits#top'].hits.hits[0]._source
   • Can reuse or follow the pattern from parseBucketsData function (SearchUtils.tsx:346)

Technical Context

The .keyword fields are indexed as lowercase (via lowercase_normalizer) so matching/filtering works case-insensitively, but _source always stores the original case. We aggregate on the lowercase .keyword for matching, and read the display value from _source via top_hits sub-aggregation to get proper case back.

Internal Reference

Slack thread: https://collate-inc.slack.com/archives/C09K5QBGG1J/p1774440697305259

[kris70lesgo]

@harshach , I would love to work on this. Could you plz assign this to me?

[harshach]

@kris70lesgo make sure to have unit tests and playwright tests for this