Enforce a bucket limit of 100 to v2 metrics calls (#20761)

Enforce a bucket count limit on metrics for v2 calls.

If people hit this limit, they should move to v3, as certain calls explode with high bucket count.

Reviewers: This *should* only affect v2 calls, but the complexity is overwhelming.

cmd/metrics-v3-types.go

@@ -267,7 +267,7 @@ func (m *MetricValues) SetHistogram(name MetricName, hist *prometheus.HistogramV
 		panic(fmt.Sprintf("metric has no description: %s", name))
 	}
 	dummyDesc := MetricDescription{}
-	metricsV2 := getHistogramMetrics(hist, dummyDesc, false)
+	metricsV2 := getHistogramMetrics(hist, dummyDesc, false, false)
 mainLoop:
 	for _, metric := range metricsV2 {
 		for label, allowedValues := range filterByLabels {