Prometheus: Introduce prometheus backend library (#83952)

* Move files to prometheus-library

* refactor core prometheus to use prometheus-library

* modify client transport options

* mock

* have a type

* import aliases

* rename

* call the right method

* remove unrelated test from the library

* update codeowners

* go work sync

* update go.work.sum

* make swagger-clean && make openapi3-gen

* add promlib to makefile

* remove clilogger

* Export the function

* update unit test

* add prometheus_test.go

* fix mock type

* use mapUtil from grafana-plugin-sdk-go

pkg/promlib/querydata/exemplar/sampler_test.go

@@ -0,0 +1,45 @@
+package exemplar_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/experimental"
+
+	"github.com/grafana/grafana/pkg/promlib/models"
+	"github.com/grafana/grafana/pkg/promlib/querydata/exemplar"
+)
+
+const update = true
+
+func TestNoOpSampler(t *testing.T) {
+	sampler := exemplar.NewNoOpSampler().(*exemplar.NoOpSampler)
+	t.Run("no-op sampler", func(t *testing.T) {
+		tr := models.TimeRange{
+			Start: time.Unix(0, 0),
+			End:   time.Unix(2000, 0),
+		}
+		ex := generateTestExemplars(tr)
+		for i := 0; i < len(ex); i++ {
+			sampler.Add(ex[i])
+		}
+		framer := exemplar.NewFramer(sampler, exemplar.NewLabelTracker())
+		experimental.CheckGoldenJSONFramer(t, "testdata", "noop_sampler", framer, update)
+	})
+}
+
+func generateTestExemplars(tr models.TimeRange) []models.Exemplar {
+	exemplars := []models.Exemplar{}
+	next := tr.Start.UTC()
+	for {
+		if next.Equal(tr.End) || next.After(tr.End) {
+			break
+		}
+		exemplars = append(exemplars, models.Exemplar{
+			Timestamp: next,
+			Value:     float64(next.Unix()),
+		})
+		next = next.Add(time.Second).UTC()
+	}
+	return exemplars
+}