Enable custom_admin_roles FF by default
What does this MR do and why?
It enables custom_admin_roles FF by default
The FF was globally enabled on gitlab.com yesterday and I also tested it on staging.
MR acceptance checklist
Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #555836 (closed)