fix(metrics): update storage metrics on gc (#2698)

Signed-off-by: Eusebiu Petu <petu.eusebiu@gmail.com>

pkg/storage/imagestore/imagestore.go

@@ -1634,6 +1634,11 @@ func (is *ImageStore) CleanupRepo(repo string, blobs []godigest.Digest, removeRe
 		}
 	}
 
+	// finally update metrics
+	if is.storeDriver.Name() == storageConstants.LocalStorageDriverName {
+		monitoring.SetStorageUsage(is.metrics, is.rootDir, repo)
+	}
+
 	return count, nil
 }