Make firewall re-check it's rules

[equetzal]

Problem

The current firewall is only executed on a directives application. This is a problem if the DNS resolution didn't worked properly, which can lead to a bad firewall application. The current solution if to run systemctl start happly to re-run the directives application.

Proposed solution

Make the firewall it's own service and set a pre-run condition that actually checks for the firewall rules and validates with the DNS resolution. If the DNS resolution is different than the expected one, re-apply the rules. We can set this as a recurrent check instead of a one shot run to avoid manually needing to re-run the task.