Like with Rails configuration files, this is pristine import of template
gitconfig from omnibus GitLab from

    https://gitlab.com/gitlab-org/omnibus-gitlab/tree/8eda093/files/gitlab-cookbooks/gitlab/templates/default

This is only a "user" part of git configuration. System-wide
configuration is generated dynamically:

    https://gitlab.com/gitlab-org/omnibus-gitlab/blob/8eda093/files/gitlab-cookbooks/gitlab/attributes/default.rb#L23

and we'll import it by hand in the follow-up patches.

/cc @kazuhiko, @jerome