metric: use cumulative count instead of windowed count in tsdb

Previously, we were writing the windowed count of a histogram into tsdb.
This meant that on each tick, the count reset. This is useful for
calculating averages and quantiles using windowed histograms, but makes
little sense to record for `count`.

This patch now uses the cumulative count in tsdb.

Informs cockroachdb#98745

Release note (bug fix): Timeseries metric counts will now show
cumulative counts for a histogram rather than the windowed count.

pkg/server/status/recorder.go

@@ -625,8 +625,9 @@ type registryRecorder struct {
 func extractValue(name string, mtr interface{}, fn func(string, float64)) error {
 	switch mtr := mtr.(type) {
 	case metric.WindowedHistogram:
+		// Use cumulative count here
+		fn(name+"-count", float64(mtr.(*metric.Histogram).TotalCount()))
 		n := float64(mtr.TotalCountWindowed())
-		fn(name+"-count", n)
 		avg := mtr.TotalSumWindowed() / n
 		if math.IsNaN(avg) || math.IsInf(avg, +1) || math.IsInf(avg, -1) {
 			avg = 0