Add certs command

[ehelms]

The idea here is to introduce a command that can stand-alone generate certificates as is done within the installer using the same logic of puppet-certs module. This intentionally does not cover deployment, it simply allows generation of the certificates. This relies upon https://github.com/theforeman/puppet-certs/pull/449 as it introduces a class that makes this process works and avoids the complication that the individual certificate classes create via their params.

The full design idea is to split generation from deployment and allow generation to happen prior to full puppet apply within the installer and allow the installer part to only handle deployment. This will put us a step closer to allowing users to provider their own certificates by standardizing on the set of certificates as inputs where those inputs can come directly from the user or from the self-generated set.