Allow read-only access to groups and projects pages in the admin area

What does this MR do and why?

Allow read-only access to groups and projects pages in the admin area for non-admin users with custom admin roles enabling read_admin_groups and read_admin_projects permissions.

References

Implements Permission to view custom attributes (or groups... (#534449 - closed).

Screenshots or screen recordings

Page	Admin	Regular user with read_admin_groups and read_admin_projects custom admin permissions
Groups list
Group page
Projects list
Project page

How to set up and validate locally

1. Enable custom_admin_roles feature flag
2. Login with an admin, enable admin mode (doc), enter admin mode, and go to http://localhost:9393/admin/application_settings/roles_and_permissions/
3. Create a custom admin role with View Groups and View Projects permissions
4. Assign custom admin role to a non-admin user (doc)
5. Login with the user
6. Go to Admin area and verify that the groups, projects, group details, and project details pages are accessible and look like the screenshots.

MR acceptance checklist

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