Pyroscope: Process and display sampling annotations (#109707)

* pyroscope: process sampling annotations

* Enable annotations in classic explore

* Run prettier

* Revert unneeded change to plugin.json

* Tweak wording in sampling annotation

* Fix test

* Disable annotations by default

pkg/tsdb/grafana-pyroscope-datasource/annotation/sampling.go

@@ -0,0 +1,47 @@
+package annotation
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type annotationWithSamplingBody struct {
+	Body profileSampledAnnotation `json:"body"`
+}
+
+type profileSampledAnnotation struct {
+	Source *samplingSource `json:"source"`
+}
+
+type samplingSource struct {
+	UsageGroup  string  `json:"usageGroup"`
+	Probability float64 `json:"probability"`
+}
+
+func convertSamplingAnnotation(raw string, timestamp int64) (*processedProfileAnnotation, error) {
+	var profileAnnotation annotationWithSamplingBody
+	err := json.Unmarshal([]byte(raw), &profileAnnotation)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing annotation data: %w", err)
+	}
+	if profileAnnotation.Body.Source == nil {
+		return nil, fmt.Errorf("error parsing sampling annotation data: source is nil")
+	}
+
+	samplingInfo := profileAnnotation.Body.Source
+	if samplingInfo.Probability == 1.0 {
+		return nil, nil
+	}
+
+	reductionPercentage := (1 - samplingInfo.Probability) * 100
+	id := fmt.Sprintf("%s-%.0f", samplingInfo.UsageGroup, reductionPercentage)
+	text := fmt.Sprintf("Profile volume reduced by %.2f%% for this service.", reductionPercentage)
+
+	return &processedProfileAnnotation{
+		id:       id,
+		text:     text,
+		time:     timestamp,
+		timeEnd:  timestamp,
+		isRegion: true,
+	}, nil
+}