Install a web interface to our monitoring software

Originally created by @bertagaz on #11194 (Redmine)

Part of the deployment of our monitoring system is to have a web interface to it.

Icingaweb2 is available in Stretch and installable from there on Jessie. Upstream offers a puppet-icingaweb2 module we can use.

As for our other internet facing services, it should work over HTTPS only, and be protected by a htpassword.

Parent Task: tails/sysadmin#8648