SSE: (Chore/Instrumentation) Add ds_queries_total metric and move met… (#66695)

* SSE: (Chore/Instrumentation) Add ds_queries_total metric and move metrics to service

pkg/expr/metrics.go

@@ -0,0 +1,47 @@
+package expr
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	metricsSubSystem = "sse"
+	metricsNamespace = "grafana"
+)
+
+type metrics struct {
+	dsRequests *prometheus.CounterVec
+
+	// older metric
+	expressionsQuerySummary *prometheus.SummaryVec
+}
+
+func newMetrics(reg prometheus.Registerer) *metrics {
+	m := &metrics{
+		dsRequests: prometheus.NewCounterVec(prometheus.CounterOpts{
+			Namespace: metricsNamespace,
+			Subsystem: metricsSubSystem,
+			Name:      "ds_queries_total",
+			Help:      "Number of datasource queries made via server side expression requests",
+		}, []string{"error", "dataplane"}),
+
+		// older (No Namespace or Subsystem)
+		expressionsQuerySummary: prometheus.NewSummaryVec(
+			prometheus.SummaryOpts{
+				Name:       "expressions_queries_duration_milliseconds",
+				Help:       "Expressions query summary",
+				Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
+			},
+			[]string{"status"},
+		),
+	}
+
+	if reg != nil {
+		reg.MustRegister(
+			m.dsRequests,
+			m.expressionsQuerySummary,
+		)
+	}
+
+	return m
+}