enh: kb metadata search

backend/open_webui/retrieval/vector/main.py

@@ -53,7 +53,11 @@ class VectorDBBase(ABC):
 
     @abstractmethod
     def search(
-        self, collection_name: str, vectors: List[List[Union[float, int]]], limit: int
+        self,
+        collection_name: str,
+        vectors: List[List[Union[float, int]]],
+        filter: Optional[Dict] = None,
+        limit: int = 10,
     ) -> Optional[SearchResult]:
         """Search for similar vectors in a collection."""
         pass