certbot: Add cron job to notify expiring certs

roles/certbot/files/check-certs.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+set -eu
+umask 077
+
+certbot certificates 2> /dev/null | awk '
+    {
+        if (/^  Certificate Name: /) { cert = $3 }
+        if (/^    Expiry Date: /) {
+            days = $6
+	    if (days < 30) {
+                print cert " " days " days"
+            }
+        }
+    }
+    '