- Download them on SR build and pass info to instance
- Instance prepares to process them as jinja2 templates
- Instance hooks the files into configuration location as appropriate

Every file so far is renamed *.erb -> *.in and a header added showing
that this file is autogenerated with links about what was the base
gitlab and/or omnibus version and omnibus reference revision this
template was last updated for.

So far all result configuration files are invalid - because ERB syntax
is there. We will convert the configuration files to proper jinja2
syntax and to using slapos parameters incrementally in the upcoming
patches.

NOTE (again): md5 sums are not yet fixed - we will fix them in the end
    of gitlab patches series after applying all tweaking changes.

/cc @kazuhiko, @jerome

Pristine import of template configuration files from omnibus GitLab
package. 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 will convert the templates to jinja2 and adjust them to slapos
version in the following patches.

Scheme for synchronizing with future upstream changes is envisioned as this:

    - checkout latest commit which updated pristine erb files
    - copy updated files from omnibus-gitlab, and commit the updates
    - checkout slapos master
    - merge commit that updated erb

That should reasonably work with not too-many conflicts and even those
should be not hard to resolve (with `git mergetool` e.g. in kdiff3)

/cc @kazuhiko, @jerome