Add dashboard for tahoe-lafs
This adds a detailed dashboard for tahoe-lafs running on one node.
It's a v1; I expect to amend it when we have real data.
It looks like this (the data in the screenshot is stale, so it does not have a lot going on):
Since JSON blobs are not super nice to review I'll just merge this and see.
Fixes privatestorageops#396.
Edited by Florian Sesser