refac: lazy load big dependencies to reduce min memory usage

backend/open_webui/apps/retrieval/vector/connector.py

@@ -1,10 +1,10 @@
-from open_webui.apps.retrieval.vector.dbs.chroma import ChromaClient
-from open_webui.apps.retrieval.vector.dbs.milvus import MilvusClient
-
-
 from open_webui.config import VECTOR_DB
 
 if VECTOR_DB == "milvus":
+    from open_webui.apps.retrieval.vector.dbs.milvus import MilvusClient
+
     VECTOR_DB_CLIENT = MilvusClient()
 else:
+    from open_webui.apps.retrieval.vector.dbs.chroma import ChromaClient
+
     VECTOR_DB_CLIENT = ChromaClient()