Address PR feedback

- Removed brittle serializer marking mechanism in favor of direct checks
  on behavior.
- Attempted to introduce a bulk_create action and then route to it on
  POST in NetBoxRouter, but ran in to several obstacles including
  breaking HTTP status code reporting in the schema. Opted to simply

contrib/openapi.json

@@ -260135,4 +260135,4 @@
             "description": "NetBox"
         }
     ]
-}
+}