Simplify auth metadata plugin

Author: NickCao

packages/jumpstarter/jumpstarter/config/grpc.py

@@ -4,15 +4,17 @@
 
 
 def call_credentials(kind: str, metadata: ObjectMeta, token: str):
-    class AuthMetadataPlugin(grpc.AuthMetadataPlugin):
-        def __call__(context: grpc.AuthMetadataContext, callback: grpc.AuthMetadataPluginCallback):
-            callback(
-                [
-                    ("jumpstarter.dev/kind", kind),
-                    ("jumpstarter.dev/namespace", metadata.namespace),
-                    ("jumpstarter.dev/name", metadata.name),
-                ],
-                None,
-            )
+    def metadata_call_credentials(context: grpc.AuthMetadataContext, callback: grpc.AuthMetadataPluginCallback):
+        callback(
+            [
+                ("jumpstarter.dev/kind", kind),
+                ("jumpstarter.dev/namespace", metadata.namespace),
+                ("jumpstarter.dev/name", metadata.name),
+            ],
+            None,
+        )
 
-    return grpc.composite_call_credentials(AuthMetadataPlugin, grpc.access_token_call_credentials(token))
+    return grpc.composite_call_credentials(
+        metadata_call_credentials,
+        grpc.access_token_call_credentials(token),
+    )