refac: vector db clients

backend/open_webui/apps/rag/vector/dbs/chroma.py

@@ -36,10 +36,10 @@ class ChromaClient:
                 database=CHROMA_DATABASE,
             )
 
-    def list_collections(self) -> list[str]:
-        # List all the collections in the database.
+    def has_collection(self, collection_name: str) -> bool:
+        # Check if the collection exists based on the collection name.
         collections = self.client.list_collections()
-        return [collection.name for collection in collections]
+        return collection_name in [collection.name for collection in collections]
 
     def delete_collection(self, collection_name: str):
         # Delete the collection based on the collection name.