[transfer] update export to use image store references

Signed-off-by: Derek McGowan <derek@mcg.dev>

pkg/transfer/transfer.go

@@ -69,9 +69,15 @@ type ImageGetter interface {
 	Get(context.Context, images.Store) (images.Image, error)
 }
 
+// ImageLookup is a type which returns images from an image store
+// based on names or prefixes
+type ImageLookup interface {
+	Lookup(context.Context, images.Store) ([]images.Image, error)
+}
+
 // ImageExporter exports images to a writer
 type ImageExporter interface {
-	Export(ctx context.Context, is images.Store, cs content.Store) error
+	Export(context.Context, content.Store, []images.Image) error
 }
 
 // ImageImporter imports an image into a content store