docs(pubsub-v1): The message_id metadata field for JavaScriptUDF is optional, not required (#29434)

Author: gcf-owl-bot[bot]

google-cloud-pubsub-v1/proto_docs/google/pubsub/v1/pubsub.rb

@@ -638,7 +638,7 @@ class ConfluentCloudFailureReason
         #       *
         #       * @param  \\{Object<string, any>} metadata - Pub/Sub message metadata.
         #       * Keys:
-        #       *   - (required) 'message_id'  : \\{string}
+        #       *   - (optional) 'message_id'  : \\{string}
         #       *   - (optional) 'publish_time': \\{string} YYYY-MM-DDTHH:MM:SSZ format
         #       *   - (optional) 'ordering_key': \\{string}
         #       */