Allow restricting Project/Repo Admins in how they can configure Branch Permissions and Exemptions

We have observed an unhealthy pattern, where Project and Repo Admins create exemptions to the Branch Permission that enforces the usage of Pull Requests. As result, the exempted users can commit directly to the branch, without a Pull Request. This goes against the best practices and our internal policies.

To help prevent this, we would like to have some way to:

• Remove all the existing exemptions from this Branch Permission (and possibly others),
• Enforce the usage of Pull Requests across all the Projects and Repositories,
• Prevent the Project/Repo Admins from adding exemptions to some/all Branch Permissions