Add Elasticsearch VDB provider to docs/providers/matris.md
The `ai_vdb_provider_elasticsearch` module (https://www.drupal.org/project/ai_vdb_provider_elasticsearch)
implements the AI Search VDB interface against Elasticsearch's native
`dense_vector` + HNSW.
Currently, it is the only Drupal VDB provider
offering native hybrid search (kNN + BM25 merged via Reciprocal Rank
Fusion) in a single Elasticsearch request.
Should be added to the matrix under the Vector Database column.
[ai-matrix-add-elasticsearch.patch](/uploads/91488730bc49c8344ddecd6762bb14a2/ai-matrix-add-elasticsearch.patch)
task