step_acme_cert: Replace with a more generic host-autorenewal-certificate role

[maxhoesel]

As discussed in #127 and #129, the current step_acme_cert role could easily be reworked to support all possible types of certificates, with automatic renewal still happening on the host through step renew.
Having such a role would provide a host-based alternative to the controller-based renewal proposed in #188.

#129 could potentially serve as a template, but with the major changes to step_ca_certificate it might be better to start from scratch. I would suggest a role that only runs step_ca_certificate, then installs the renewal daemon.

To-Dos:

• Wait for Add step_certificate role, supporting multiple provisioners #129 to be implemented
• Decide on a name - step_certificate would conflict with a potential future module. Maybe host_certificate?
• Decide on how to pass parameters to the step_ca_certificate call
• Also implement rekeying