Add a new pagure_authorized_keys service
This is the service that will managed the authorized_keys file when
using the ``pagure_authorized_keys`` auth backend.
Enable this service in the vagrant-based dev environment
Include a production-ready version of this service in the `files/` folder
to be included in the releases.
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>