[#373] fstree: Add metrics

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

pkg/local_object_storage/blobstor/fstree/control.go

@@ -7,6 +7,7 @@ import (
 // Open implements common.Storage.
 func (t *FSTree) Open(ro bool) error {
 	t.readOnly = ro
+	t.metrics.SetMode(ro)
 	return nil
 }
 
@@ -16,4 +17,7 @@ func (t *FSTree) Init() error {
 }
 
 // Close implements common.Storage.
-func (*FSTree) Close() error { return nil }
+func (t *FSTree) Close() error {
+	t.metrics.Close()
+	return nil
+}