Show available private groups in the list of all groups

[davidmz]

If a user is authorized, the page https://freefeed.net/all-groups should show the private groups available to them. They should be marked with a special icon (this will require a modification in freefeed-react-client).

[amanx123]

Please allow me to work on this. Assign me

[davidmz]

@amanx123 Sure) You need to change the GroupsController.allGroups method. Please don't forget to add tests for your changes.