feat(hunspell): Add ref_path support and cache invalidation API

- Add ref_path parameter for package-based dictionary loading
- Load from config/packages/{packageId}/hunspell/{locale}/
- Add cache info API: GET /_hunspell/cache (cluster:monitor/hunspell/cache)
- Add cache invalidation API: POST /_hunspell/cache/_invalidate (cluster:admin/hunspell/cache/invalidate)
- Support invalidation by package_id, locale, cache_key, or invalidate_all
- Add security validation (path traversal, separator injection, null bytes)
- Add updateable flag for hot-reload via _reload_search_analyzers
- Use Strings.hasText() and Strings.isNullOrEmpty() for validation consistency
- Consistent response schema with all fields always present
- Add unit tests, REST handler tests, and integration tests

Signed-off-by: shayush622 <ayush5267@gmail.com>

Author: shayush622

CHANGELOG.md

@@ -38,6 +38,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Introduced strategy planner interfaces for indexing and deletion ([#20585](https://github.com/opensearch-project/OpenSearch/pull/20585))
 - Implement FieldMappingIngestionMessageMapper for pull-based ingestion ([#20729](https://github.com/opensearch-project/OpenSearch/pull/20729))
 - Add ref_path support for package-based hunspell dictionary loading and cache invalidation API ([#20741](https://github.com/opensearch-project/OpenSearch/pull/20741))
+- Add ref_path support for package-based hunspell dictionary loading and cache invalidation API ([#20792](https://github.com/opensearch-project/OpenSearch/pull/20792))
 
 ### Changed
 - Move Randomness from server to libs/common ([#20570](https://github.com/opensearch-project/OpenSearch/pull/20570))