Allow group owners and GitLab admins to create public projects within private groups

It appears as though even admins are unable to change the visibility level of projects in a group to a level higher than the group is set to.

It is quite normal, I believe, for a group to want to be private but still have a few projects public and clone-able without authentication. Also, I believe this used to work just fine before. I am now running into the problem for the first time with projects that were set to public but that I cannot now re-set to public because the group is private (after first running into the problem that I couldn't set the group to private because there were public projects.)

Since admins are not otherwise subject to visibility restrictions, I believe this restriction should also be removed for admins.