fix for container name

Author: Gaudy Blanco

docs/config/yaml.md

@@ -197,7 +197,6 @@ For example:
 vector_store:
   type: lancedb
   db_uri: output/lancedb
-  container_name: christmas-carol
   index_prefix: "christmas-carol"
   embeddings_schema:
     text_unit.text:

graphrag/config/defaults.py

@@ -372,7 +372,7 @@ class VectorStoreDefaults:
     type: ClassVar[str] = VectorStoreType.LanceDB.value
     db_uri: str = str(Path(DEFAULT_OUTPUT_BASE_DIR) / "lancedb")
     overwrite: bool = True
-    index_prefix: None = None
+    index_prefix: str = ""
     url: None = None
     api_key: None = None
     audience: None = None