Internationalisation of groups directory

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

app/assets/javascripts/groups/transfer_dropdown.js

 import $ from 'jquery';
+import { __ } from '~/locale';
 
 export default class TransferDropdown {
   constructor() {
@@ -13,7 +14,7 @@ export default class TransferDropdown {
   }
 
   buildDropdown() {
-    const extraOptions = [{ id: '', text: 'No parent group' }, 'divider'];
+    const extraOptions = [{ id: '', text: __('No parent group') }, 'divider'];
 
     this.groupDropdown.glDropdown({
       selectable: true,

locale/gitlab.pot

@@ -6038,6 +6038,9 @@ msgstr ""
 msgid "No other labels with such name or description"
 msgstr ""
 
+msgid "No parent group"
+msgstr ""
+
 msgid "No preview for this file type"
 msgstr ""