feat: support better qdrant collection isolation

The prefix string for qdrant collection is now
configurable,  which means the same qdrant cluster
can be used to host more open webui instances and
to be able to separate the collections between the
different owui instances.

backend/open_webui/config.py

@@ -1799,6 +1799,7 @@ QDRANT_GRPC_PORT = int(os.environ.get("QDRANT_GRPC_PORT", "6334"))
 ENABLE_QDRANT_MULTITENANCY_MODE = (
     os.environ.get("ENABLE_QDRANT_MULTITENANCY_MODE", "false").lower() == "true"
 )
+QDRANT_COLLECTION_PREFIX = os.environ.get("QDRANT_COLLECTION_PREFIX", "open-webui")
 
 # OpenSearch
 OPENSEARCH_URI = os.environ.get("OPENSEARCH_URI", "https://localhost:9200")