Optimized nginx CSP (prop. leads to problems due to too high restrictions for some roles) and implemented health check for mailer

roles/health-msmtp/templates/health-msmtp.sh.j2

@@ -0,0 +1,4 @@
+#!/bin/bash
+echo "Subject: $HOST is alive
+
+Host $HOSTNAME reports at $(date): I'm alive." | msmtp -t {{ users.administrator.email }}