feat: add memo field to UpdateScheduleRequest

Adds Memo field (field 8) to UpdateScheduleRequest with merge
semantics for updating schedule memo on CHASM-backed schedules.

Author: chaptersix

temporal/api/workflowservice/v1/request_response.proto

@@ -1355,6 +1355,13 @@ message UpdateScheduleRequest {
     // Note: you cannot only update the search attributes with `UpdateScheduleRequest`,
     // you must also set the `schedule` field; otherwise, it will unset the schedule.
     temporal.api.common.v1.SearchAttributes search_attributes = 7;
+
+    // Schedule memo to update. Uses merge semantics:
+    // - Fields with non-nil values are upserted.
+    // - Fields with nil/empty values are deleted.
+    // - Fields not present are left unchanged.
+    // Do not set this field if you do not want to update the memo.
+    temporal.api.common.v1.Memo memo = 8;
 }
 
 message UpdateScheduleResponse {