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/recipes/systemd_emails.rb

@@ -0,0 +1,45 @@
+#
+# Cookbook Name:: kosmos-base
+# Recipe:: systemd_emails
+#
+# The MIT License (MIT)
+#
+# Copyright:: 2019, Kosmos Developers
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+# To add email notifications to a Systemd service, add the following entry to
+# the [Unit] section of its service:
+#
+# OnFailure=status-email-ops@%n.service
+
+cookbook_file "/usr/local/sbin/systemd-email" do
+  source "systemd-email"
+  mode "750"
+end
+
+template "/etc/systemd/system/status-email-ops@.service" do
+  source "status-email-ops@.service"
+  variables email: "ops@kosmos.org"
+end
+
+execute "systemctl daemon-reload" do
+  command "systemctl daemon-reload"
+  action :nothing
+end