Add service client

Author: samwelkanda

msgraph/graph_service_client.py

@@ -0,0 +1,6 @@
+from .generated import BaseGraphClient
+from .graph_request_adapter import BaseGraphRequestAdapter
+
+class GraphServiceClient(BaseGraphClient):
+    def __init__(self, request_adapter: BaseGraphRequestAdapter) -> None:
+        super().init(request_adapter)