[prometheusreceiver] Handle staleNaN for up metric

When a target disappears, a StaleNaN is added. We should handle that case too.

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

receiver/prometheusreceiver/internal/otlp_metricsbuilder.go

@@ -23,6 +23,7 @@ import (
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/model/textparse"
+	"github.com/prometheus/prometheus/model/value"
 	"go.opentelemetry.io/collector/pdata/pmetric"
 	"go.uber.org/zap"
 )
@@ -154,7 +155,8 @@ func (b *metricBuilderPdata) AddDataPoint(ls labels.Labels, t int64, v float64)
 		lm := ls.Map()
 		// See https://www.prometheus.io/docs/concepts/jobs_instances/#automatically-generated-labels-and-time-series
 		// up: 1 if the instance is healthy, i.e. reachable, or 0 if the scrape failed.
-		if metricName == scrapeUpMetricName && v != 1.0 {
+		// But it can also be a staleNaN, which is inserted when the target goes away.
+		if metricName == scrapeUpMetricName && v != 1.0 && !value.IsStaleNaN(v) {
 			if v == 0.0 {
 				b.logger.Warn("Failed to scrape Prometheus endpoint",
 					zap.Int64("scrape_timestamp", t),