[#370] Add tree service metrics

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

pkg/metrics/node.go

@@ -1,6 +1,9 @@
 package metrics
 
-import "github.com/prometheus/client_golang/prometheus"
+import (
+	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/services/tree"
+	"github.com/prometheus/client_golang/prometheus"
+)
 
 const namespace = "frostfs_node"
 
@@ -9,9 +12,10 @@ type NodeMetrics struct {
 	engineMetrics
 	stateMetrics
 	replicatorMetrics
-	epoch metric[prometheus.Gauge]
 
 	writeCacheMetrics *writeCacheMetrics
+	treeService       *treeServiceMetrics
+	epoch             metric[prometheus.Gauge]
 }
 
 func NewNodeMetrics() *NodeMetrics {
@@ -27,6 +31,9 @@ func NewNodeMetrics() *NodeMetrics {
 	replicator := newReplicatorMetrics()
 	replicator.register()
 
+	treeService := newTreeServiceMetrics()
+	treeService.register()
+
 	epoch := newGauge(prometheus.GaugeOpts{
 		Namespace: namespace,
 		Subsystem: innerRingSubsystem,
@@ -43,6 +50,7 @@ func NewNodeMetrics() *NodeMetrics {
 		engineMetrics:        engine,
 		stateMetrics:         state,
 		replicatorMetrics:    replicator,
+		treeService:          treeService,
 		epoch:                epoch,
 		writeCacheMetrics:    writeCacheMetrics,
 	}
@@ -60,3 +68,7 @@ func (m *NodeMetrics) WriteCache() WriteCacheMetrics {
 	}
 	return m.writeCacheMetrics
 }
+
+func (m *NodeMetrics) TreeService() tree.MetricsRegister {
+	return m.treeService
+}