Restrict protected branch deletion to Owners / No One
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### Release notes
Previously, Protected branches could be deleted by [Maintainer-level users and above](https://docs.gitlab.com/ee/user/project/protected_branches.html#delete-a-protected-branch) via the UI or API. This new feature provides further restrictions on the ability to delete protected branches to only project Owners. Additionally, this setting can now be enforced via inheritance to apply to [all projects in a group](https://docs.gitlab.com/ee/user/project/protected_branches.html#for-all-projects-in-a-group) to further restrict the ability to delete a protected branch.
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### Problem to solve
A [Large Saas Customer](https://gitlab.zendesk.com/agent/tickets/540815) contacted Support in [this ticket](https://gitlab.zendesk.com/agent/tickets/540815) to indicate their interest in additional features regarding protected branches. Specifically, they would like to see:
- An option to update protected branch deletion protection to only Owners (or "No one", requiring a settings change to make the option available again in the UI), to limit deletion capability for Maintainers.
- The ability to enforce this deletion at a higher group level, to apply to all subgroups and projects.
### Intended users
* [Delaney (Development Team Lead)](https://handbook.gitlab.com/handbook/product/personas/#delaney-development-team-lead)
### Available Tier
* Premium
* Ultimate
issue