Allow creating groups without members

[lukasrad02]

Is your feature request related to a problem? Please describe.

Sometimes, I want to create a group without any members, for example to make this group responsible for events although the user accounts of the members have not been created yet.

Unfortunately, the user select is a required field on the group creation view, and therefore it is not allowed to keep it empty.

Describe the solution you'd like

Allow creating groups without members by making the user select not required.

Describe alternatives you've considered

As an alternative, I could add some arbitrary user to the group while creating it and remove it (via the user edit view) afterwards. However, this is cumbersome and, if forgotten, could lead to wrong permissions.

Additional context

Due to the restriction discussed above, it is also not possible to edit (rename, change permissions, …) of empty group without adding a user.