[#412] node: Replace metrics package

Use observability module.

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

pkg/metrics/node.go

@@ -2,6 +2,7 @@ package metrics
 
 import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/services/tree"
+	"git.frostfs.info/TrueCloudLab/frostfs-observability/metrics"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -15,39 +16,31 @@ type NodeMetrics struct {
 
 	writeCacheMetrics *writeCacheMetrics
 	treeService       *treeServiceMetrics
-	epoch             metric[prometheus.Gauge]
+	epoch             prometheus.Gauge
 	gc                *gcMetrics
 }
 
 func NewNodeMetrics() *NodeMetrics {
 	objectService := newObjectServiceMetrics()
-	objectService.register()
 
 	engine := newEngineMetrics()
-	engine.register()
 
 	state := newStateMetrics()
-	state.register()
 
 	replicator := newReplicatorMetrics()
-	replicator.register()
 
 	treeService := newTreeServiceMetrics()
-	treeService.register()
 
-	epoch := newGauge(prometheus.GaugeOpts{
+	epoch := metrics.NewGauge(prometheus.GaugeOpts{
 		Namespace: namespace,
 		Subsystem: innerRingSubsystem,
 		Name:      "epoch",
 		Help:      "Current epoch as seen by inner-ring node.",
 	})
-	mustRegister(epoch)
 
 	writeCacheMetrics := newWriteCacheMetrics()
-	writeCacheMetrics.register()
 
 	gc := newGCMetrics()
-	gc.register()
 
 	return &NodeMetrics{
 		objectServiceMetrics: objectService,
@@ -63,7 +56,7 @@ func NewNodeMetrics() *NodeMetrics {
 
 // SetEpoch updates epoch metric.
 func (m *NodeMetrics) SetEpoch(epoch uint64) {
-	m.epoch.value.Set(float64(epoch))
+	m.epoch.Set(float64(epoch))
 }
 
 // WriteCache returns WriteCache metrics.