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/templates/default/status-email-ops@.service

@@ -0,0 +1,8 @@
+[Unit]
+Description=status email for %i to ops
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/systemd-email <%= @email %> %i
+User=root
+Group=systemd-journal