server: add time series for disk and net IO stats

Use new library `gopsutil` to gather IO stats from the host kernel and
save them as time series.

Caveat: these counters are for the entire host over its lifetime. As
such, the first value cockroach records may be very high, and if we plot
these charts as derivatives, the derivative from zero to the first
recorded data point will be much higher than subsequent derivatives,
making a plot where it's hard to see changes after that.

A future commit will gather per-process IO stats, but gopsutil only
provides that on Linux.

Release note (admin ui change): gather disk and network IO statistics and
save them as time series.

pkg/server/server.go

@@ -431,7 +431,7 @@ func NewServer(cfg Config, stopper *stop.Stopper) (*Server, error) {
 	s.recorder = status.NewMetricsRecorder(s.clock, s.nodeLiveness, s.rpcContext, s.gossip, st)
 	s.registry.AddMetricStruct(s.rpcContext.RemoteClocks.Metrics())
 
-	s.runtime = status.MakeRuntimeStatSampler(s.clock)
+	s.runtime = status.MakeRuntimeStatSampler(ctx, s.clock)
 	s.registry.AddMetricStruct(s.runtime)
 
 	s.node = NewNode(