Consider Moving Restricting Push and Merge Access to Certain Users to Core

For users with integration users on their projects - allowing them to set restrictions on the Push to protected branches would enable them to appropriately provision a integration user with Developer permissions that could still post build status back to the protected branch while limiting the users overall settings and blocking them from merging.

• Current Feature Docs Link - https://docs.gitlab.com/ee/user/project/protected_branches.html#restricting-push-and-merge-access-to-certain-users-starter
• User Reference - #213626 (comment 322660518)