cloud-cleaner: clean up GCP Storage objects based on metadata

Add StorageListObjectsByMetadata() to internal GCP library. The method
allows one to search specific Storage bucket for objects based on
provided metadata.

Extend cloud-cleaner to search for any Storage objects related to the
image import, using custom metadata set on the object. Delete all found
objects.

Signed-off-by: Tomas Hozza <thozza@redhat.com>

internal/cloud/gcp/storage.go

@@ -196,3 +196,54 @@ func (g *GCP) StorageImageImportCleanup(imageName string) ([]string, []error) {
 
 	return deletedObjects, errors
 }
+
+// StorageListObjectsByMetadata searches specified Storage bucket for objects matching the provided
+// metadata. The provided metadata is used for filtering the bucket's content. Therefore if the provided
+// metadata is nil, then all objects present in the bucket will be returned.
+//
+// Matched objects are returned as a list of ObjectAttrs.
+//
+// Uses:
+//	- Storage API
+func (g *GCP) StorageListObjectsByMetadata(bucket string, metadata map[string]string) ([]*storage.ObjectAttrs, error) {
+	var matchedObjectAttr []*storage.ObjectAttrs
+	ctx := context.Background()
+
+	storageClient, err := storage.NewClient(ctx, option.WithCredentials(g.creds))
+	if err != nil {
+		return nil, fmt.Errorf("failed to get Storage client: %v", err)
+	}
+	defer storageClient.Close()
+
+	objects := storageClient.Bucket(bucket).Objects(ctx, nil)
+	for {
+		obj, err := objects.Next()
+		if err == iterator.Done {
+			break
+		}
+		if err != nil {
+			return nil, fmt.Errorf("failure while iterating over bucket objects: %v", err)
+		}
+
+		// check if the object's Metadata match the provided values
+		metadataMatch := true
+		for key, value := range metadata {
+			objMetadataValue, ok := obj.Metadata[key]
+			if !ok {
+				metadataMatch = false
+				break
+			}
+			if objMetadataValue != value {
+				metadataMatch = false
+				break
+			}
+		}
+
+		if metadataMatch {
+			matchedObjectAttr = append(matchedObjectAttr, obj)
+		}
+
+	}
+
+	return matchedObjectAttr, nil
+}