[#376] metrics: Add GC metrics

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

pkg/metrics/node.go

@@ -16,6 +16,7 @@ type NodeMetrics struct {
 	writeCacheMetrics *writeCacheMetrics
 	treeService       *treeServiceMetrics
 	epoch             metric[prometheus.Gauge]
+	gc                *gcMetrics
 }
 
 func NewNodeMetrics() *NodeMetrics {
@@ -45,6 +46,9 @@ func NewNodeMetrics() *NodeMetrics {
 	writeCacheMetrics := newWriteCacheMetrics()
 	writeCacheMetrics.register()
 
+	gc := newGCMetrics()
+	gc.register()
+
 	return &NodeMetrics{
 		objectServiceMetrics: objectService,
 		engineMetrics:        engine,
@@ -53,6 +57,7 @@ func NewNodeMetrics() *NodeMetrics {
 		treeService:          treeService,
 		epoch:                epoch,
 		writeCacheMetrics:    writeCacheMetrics,
+		gc:                   gc,
 	}
 }
 
@@ -72,3 +77,7 @@ func (m *NodeMetrics) WriteCache() WriteCacheMetrics {
 func (m *NodeMetrics) TreeService() tree.MetricsRegister {
 	return m.treeService
 }
+
+func (m *NodeMetrics) GC() GCMetrics {
+	return m.gc
+}