🔀 refactor(base.py): add from_method_nodes dictionary to RetrieverCreator class

The `from_method_nodes` dictionary is added to the `RetrieverCreator` class in order to map the "MultiQueryRetriever" node to the "from_llm" method. This refactor improves the readability and maintainability of the code by explicitly defining the mapping between nodes and methods.

src/backend/langflow/interface/retrievers/base.py

@@ -13,6 +13,8 @@ from langflow.utils.util import build_template_from_method
 class RetrieverCreator(LangChainTypeCreator):
     type_name: str = "retrievers"
 
+    from_method_nodes = {"MultiQueryRetriever": "from_llm"}
+
     @property
     def frontend_node_class(self) -> Type[RetrieverFrontendNode]:
         return RetrieverFrontendNode