chore: add memo content length limit setting

proto/api/v1/workspace_setting_service.proto

@@ -96,6 +96,8 @@ message WorkspaceMemoRelatedSetting {
   bool disallow_public_visible = 1;
   // display_with_update_time orders and displays memo with update time.
   bool display_with_update_time = 2;
+  // content_length_limit is the limit of content length.
+  int64 content_length_limit = 3;
 }
 
 message ListWorkspaceSettingsRequest {}