GitLab EE extends Member#add_user by adding some LDAP specific flags.
Prior to these changes, the only way this could be done was by modifying
Member#add_user in place. This could lead to merge conflicts whenever a
developer wants to change this method.

To resolve this issue, the logic that EE extends has been moved into a
separate method with the appropriate arguments. This allows EE to extend
the logic by prepending the method using an EE specific module.