certbot: add possibility to specify commands to run on new certs

This makes it possible to e.g. reload nginx when new certificates are
present.

playbooks/roles/certbot/templates/renewal_deploy_hook_commands.sh.j2

@@ -0,0 +1,4 @@
+#!/bin/bash
+{% for command in certbot__new_cert_commands %}
+{{ command }}
+{% endfor %}