Set Gitlab::Shell#create_repository as OPT_OUT
On .com repositories are created through Gitaly for a while now. For customers this is not the case unless these have chosen to do so through feature flags. By moving this to opt out, everyone will be using this. This move is part of the migration issue https://gitlab.com/gitlab-org/gitaly/issues/593 The bigger impact this commit will have is that tests that use a repository through `FactoryBot.create(:project, :repository)` will now use Gitaly to do so. As tests run on the same disk, or at least machine, this will most probably slow them down.