Move group list from /server-info to /update-groups endpoint

[Derkades]

The global group list for the groups dropdown in StaffCP > API > Group sync is currently still sent as part of the /server-info request. This is confusing for users, as they need to enable group sync as well as the server data sender for group sync to work.

[samerton]

@Derkades do you recall if this is resolved by #3538 ?

[Derkades]

No, I don't remember that PR changing anything related to the Discord role list, so it is not resolved yet. But this is only a minor issue so it can be removed from the 2.2.0 milestone in my opinion