add translation for errors checking group name (#27196)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/user.go

@@ -1226,10 +1226,10 @@ func (a *App) isUniqueToGroupNames(val string) *model.AppError {
 	var notFoundErr *store.ErrNotFound
 	group, err := a.Srv().Store().Group().GetByName(val, model.GroupSearchOpts{})
 	if err != nil && !errors.As(err, &notFoundErr) {
-		return model.NewAppError("isUniqueToGroupNames", model.NoTranslation, nil, "", http.StatusInternalServerError).Wrap(err)
+		return model.NewAppError("isUniqueToGroupNames", "app.user.save.groupname.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
 	}
 	if group != nil {
-		return model.NewAppError("isUniqueToGroupNames", model.NoTranslation, nil, fmt.Sprintf("group name %s exists", val), http.StatusBadRequest)
+		return model.NewAppError("isUniqueToGroupNames", "app.user.save.username_exists.app_error", nil, fmt.Sprintf("group name %s exists", val), http.StatusBadRequest)
 	}
 	return nil
 }

server/i18n/en.json

@@ -6830,6 +6830,10 @@
     "id": "app.user.save.existing.app_error",
     "translation": "Must call update for existing user."
   },
+  {
+    "id": "app.user.save.groupname.app_error",
+    "translation": "Unable to determine if that username already exists"
+  },
   {
     "id": "app.user.save.username_exists.app_error",
     "translation": "An account with that username already exists."