distro/Manifest: generalize the size argument

When generating an osbuild manifest for an image type, we take a
customizations struct, which specifies the image-type-independent
customizations to apply. We also take the size argument, which is
specific to the image build and not part of the blueprint.

Introduce a new argument ImageOptions, which for now just wraps the size
argument. These options are specific to the image build/type, and
therefore does not belong with the other customizations.

For now this is a non-functional change, but follow-up commits will
introduce more types of image options.

Signed-off-by: Tom Gundersen <teg@jklm.no>

internal/weldr/api.go

@@ -1603,7 +1603,13 @@ func (api *API) composeHandler(writer http.ResponseWriter, request *http.Request
 	}
 
 	size := imageType.Size(cr.Size)
-	manifest, err := imageType.Manifest(bp.Customizations, api.allRepositories(), packages, buildPackages, size)
+	manifest, err := imageType.Manifest(bp.Customizations,
+		distro.ImageOptions{
+			Size: size,
+		},
+		api.allRepositories(),
+		packages,
+		buildPackages)
 	if err != nil {
 		errors := responseError{
 			ID:  "ManifestCreationFailed",