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>