Add email notifications for failed certbot runs

Based on https://wiki.archlinux.org/index.php/Systemd/Timers#MAILTO

This can easily be used by other services, with one line added to the
[Unit] section of a service:

OnFailure=status-email-ops@%n.service

Refs #3

site-cookbooks/kosmos-base/files/default/systemd-email

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+/usr/sbin/sendmail -t <<ERRMAIL
+To: $1
+From: systemd <root@$HOSTNAME>
+Subject: $2
+Content-Transfer-Encoding: 8bit
+Content-Type: text/plain; charset=UTF-8
+
+$(systemctl status --full "$2")
+ERRMAIL