Like with Rails configuration this first step is pristine import of
nginx configuration files from omnibus-gitlab. All files were imported
as-is in their ERB form and filenames from omnibus-gitlab
8.2.3+ce.0-0-g8eda093 from here:

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

We import only nginx main http configuration - nginx's CI and Mattermost
configurations are not imported, as we do not support CI and Mattermost (yet ?).

As with Rails configuration files, we will convert the templates to
jinja2 and adjust them to slapos version in the following patches.  We
will also use the same (commit from last-erb-mod commit + merge)
approach to track upstream changes.

/cc @kazuhiko, @jerome