Add group and role creation errors handling

Currently no error handling when a failure happens while trying to create a role or a group as admin.

To-do's:

• Add or correct notifications on both pages

added Frontend label

changed title from Create/Fix group creation errors handling to Add group and role creation errors handling

changed the description

changed the description

marked the checklist item Add or correct notifications on both pages as completed

mentioned in merge request !20 (merged)

mentioned in merge request !19