We should have better docs about how we monitor Puppet server and agents
with Prometheus...

puppet server 7 uses a separate vardir location from the agent

See team#41819

There's a section about finding information in Nagios which I don't know
how to translate to prometheus, so I left it there, but we'll want to
remove and/or review that.

We're splitting the alert for hosts being unreachable / unresponsive so
that we can have a better severity level and instructions for how to
handle this case.

Unreachable hosts can be caused by a number of things so it's important
to systematically investigate what's happening.

the more I look into this, the more I think this *and* our Let's Encrypt
"special template" setup can and should be simplified using custom
Puppet server mount points, see team#41919

Asked by irl on IRC.

refs team#41254 team#41917

update references to the ENC which was moved from tor-puppet.git into
its own, separate, repository