Allow Group Admins to receive the "Contributor user limit reached" email notification

Description -

Why is this feature important to you - We have group admins who monitor end user license allocations and it would be helpful for them to receive this system generated email notification so they are aware of use cases where we might need to budget for additional light licenses. 

How would you like the feature to work - Specific group administrators should optionally be able to receive this email notification.

Current Behaviour - Only system admins receive this email notification.