Document energy monitoring infrastructure

[patricoferris]

Follow up requests from #45 .

• Tag individual machines as being monitored in a certain way.
• Have a single page explaining the monitoring methods that the first point can reference.
• Also explain the short-comings of the approaches we currently use.
• Document possible approaches for machines that are not currently monitored.
• Export the raw/summary data from Grafana/Prometheus somewhere publicly accessible -- this includes backing up this data which is currently being rewritten every 2 weeks or so I think.

[avsm]

I'm assigning this to you as "owner", Patrick -- not intending that you have to do all of the checklist yourself!