[#451] metrics: Move to internal

`metrics` don't look like something others want to import.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

internal/metrics/grpc.go

@@ -0,0 +1,35 @@
+package metrics
+
+import (
+	"git.frostfs.info/TrueCloudLab/frostfs-observability/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type GrpcServerMetrics interface {
+	MarkHealthy(endpoint string)
+	MarkUnhealthy(endpoint string)
+}
+
+type grpcServerMetrics struct {
+	endpointHealth *prometheus.GaugeVec
+}
+
+func newGrpcServerMetrics() *grpcServerMetrics {
+	return &grpcServerMetrics{
+		endpointHealth: metrics.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Namespace: namespace,
+				Subsystem: grpcServerSubsystem,
+				Name:      "health",
+				Help:      "GRPC Server Endpoint health",
+			}, []string{endpointLabel}),
+	}
+}
+
+func (m *grpcServerMetrics) MarkHealthy(endpoint string) {
+	m.endpointHealth.With(prometheus.Labels{endpointLabel: endpoint}).Set(float64(1))
+}
+
+func (m *grpcServerMetrics) MarkUnhealthy(endpoint string) {
+	m.endpointHealth.With(prometheus.Labels{endpointLabel: endpoint}).Set(float64(0))
+}