Transfer groundControl (and admin panel) from staff to admin route

[josh1248]

Accompanies the frontend pull request at https://github.com/source-academy/frontend/pull/3043

Previously, "admin" routes were available to both staff and admins to access.

Now, a new "staff" route has been created that accepts most of the previous functions. The remaining functions in "admin" scope have the ability to cause massive damage, such as the deletion of entire assessments. Hence, they are now inaccessible to avengers even if they bypass the frontend route checking.

Aside: I have also shifted admin panel actions into this admin scope.