gitlab: Import gitconfig from omnibus-gitlab

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

software/gitlab/template/gitconfig.erb

+# This file is managed by gitlab-ctl. Manual changes will be
+# erased! To change the contents below, edit /etc/gitlab/gitlab.rb
+# and run `sudo gitlab-ctl reconfigure`.
+
+[user]
+        name = <%= node['gitlab']['user']['git_user_name'] %>
+        email = <%= node['gitlab']['user']['git_user_email'] %>
+[core]
+        autocrlf = input