Target: expose osbuild artifact information in target result

Add the information about osbuid artifact to the target result.
Specifically the name of the osbuild pipeline which was exported for the
specific target, and the filename of the exported file.

This will later enable embedding this information in Koji build metadata
to make it easy to reproduce the image build using the attached
manifest.

internal/cloudapi/v2/v2_test.go

@@ -1261,6 +1261,9 @@ func TestImageFromCompose(t *testing.T) {
 	tr := target.NewAWSTargetResult(&target.AWSTargetResultOptions{
 		Ami:    "ami-abc123",
 		Region: "eu-central-1",
+	}, &target.OsbuildArtifact{
+		ExportFilename: "image.raw",
+		ExportName:     "image",
 	})
 	res, err := json.Marshal(&worker.OSBuildJobResult{
 		Success:       true,