[#373] blobovnicza: Add metrics

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

pkg/local_object_storage/blobovnicza/metrics.go

@@ -0,0 +1,16 @@
+package blobovnicza
+
+type Metrics interface {
+	IncOpenCount()
+	DecOpenCount()
+
+	IncSize(size uint64)
+	DecSize(size uint64)
+}
+
+type noopMetrics struct{}
+
+func (m *noopMetrics) IncOpenCount()  {}
+func (m *noopMetrics) DecOpenCount()  {}
+func (m *noopMetrics) IncSize(uint64) {}
+func (m *noopMetrics) DecSize(uint64) {}