The userRow in User Management needs a way to register menu entries

[blizzz]

otherwise apps like impersonate cannot add an entry anymore. Cf. nextcloud/impersonate#53

[nextcloud-bot]

GitMate.io thinks possibly related issues are #616 (Ctrl-click on entries in the user menu will keep spinner spinning), #4643 (Contacts in contact menu needs to be merged), #10283 (User management polishing), #7682 (Popover misplaced in user management), and #7424 (Allow to set language in the user management).