use default module to simplify retriever config

Author: stellasia

examples/question_answering/simple_rag_pipeline_config.json

@@ -41,7 +41,7 @@
         }
     },
     "retriever": {
-        "class_": "neo4j_graphrag.retrievers.VectorRetriever",
+        "class_": "VectorRetriever",
         "params_": {
             "driver": {
                 "resolver_": "CONFIG_KEY",

src/neo4j_graphrag/experimental/pipeline/config/template_pipeline/simple_rag_pipeline.py

@@ -34,6 +34,8 @@ class RetrieverConfig(ObjectConfig[RetrieverWrapper]):
     # the result of _get_class is a Retriever
     # it is translated into a RetrieverWrapper (which is a Component)
     # in the 'parse' method below
+    DEFAULT_MODULE = "neo4j_graphrag.retrievers"
+    REQUIRED_PARAMS = ["driver"]
 
     def parse(self, resolved_data: Optional[dict[str, Any]] = None) -> RetrieverWrapper:
         retriever = cast(Retriever, super().parse(resolved_data))