This adds a detailed dashboard for tahoe-lafs running on one node.

Response time, probe fails and TLS expiry incl. alerts.

This change reflects my intention of having an alert fire when a node
is not scrapable for five minutes or longer.  I hadn't understood the
default avg() function well enough before, yielding an alert that would
fire too soon (i.e. any time a node was down, even only one minute for a
reboot).

Fixes privatestorageops#358.

This changes the Throughput graph to be relative, changes its unit
to Bit/s, and fixes the labels of the Network pkt/s graph.

Fixes privatestorageops#24.

Fixes privatestorageops#355.

Only dashboards in this dir