[#376] metrics: Add GC metrics

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

pkg/local_object_storage/shard/delete.go

@@ -21,7 +21,9 @@ type DeletePrm struct {
 }
 
 // DeleteRes groups the resulting values of Delete operation.
-type DeleteRes struct{}
+type DeleteRes struct {
+	deleted uint64
+}
 
 // SetAddresses is a Delete option to set the addresses of the objects to delete.
 //
@@ -53,10 +55,11 @@ func (s *Shard) delete(ctx context.Context, prm DeletePrm) (DeleteRes, error) {
 		return DeleteRes{}, ErrDegradedMode
 	}
 
+	result := DeleteRes{}
 	for _, addr := range prm.addr {
 		select {
 		case <-ctx.Done():
-			return DeleteRes{}, ctx.Err()
+			return result, ctx.Err()
 		default:
 		}
 
@@ -65,11 +68,12 @@ func (s *Shard) delete(ctx context.Context, prm DeletePrm) (DeleteRes, error) {
 		s.deleteFromBlobstorSafe(ctx, addr)
 
 		if err := s.deleteFromMetabase(ctx, addr); err != nil {
-			return DeleteRes{}, err // stop on metabase error ?
+			return result, err // stop on metabase error ?
 		}
+		result.deleted++
 	}
 
-	return DeleteRes{}, nil
+	return result, nil
 }
 
 func (s *Shard) deleteObjectFromWriteCacheSafe(ctx context.Context, addr oid.Address) {