Use https for rubygems
Allow artefact registration to support whitehall slugs

This needs to support slugs with consecutive '-'s in them, and
aditionally some with a .locale suffix.

The former is addressed by the content_models bump, whereas the latter
additionally needed support in the routes.

Fixes [#67540714, #67541692]
Merge pull request #138 from alphagov/fix_artefact_registraion

Allow artefact registration to support whitehall slugs