Add group of Instance Administrators

Problem to solve

Currently, all admins are directly added as maintainers of the self-monitoring project (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14511#note_192538664).

Instead, we can create a group and add all admins as members. Then, that group can be granted maintainer permissions to the self-monitoring project.

Another option is (as suggested by @sarahwaldner - https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14511#note_192453494):

1. Create a new group (at the same time as the new project) called Instance Administrators (or something else)
2. Create the self-monitoring project in that group so that all users who are members of that group have permissions of Owner/Maintainer in the new project.
3. Customers can then control who has access to the new self-monitoring project

Intended users

Further details

Proposal

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references