Disable new user sign-up by default
Background: By default, new GitLab self-hosted installations have new user sign-up enabled.
Problem: With the defaults settings, external or unwanted users can create new user accounts. The new accounts are added to the customer's true-up count and can be used to login to the instance if sign-up restrictions are not implemented.
Make "Sign up enabled" off by default and require admin action to enable it.