cmd/gen-manifests: add package-sets to repo config

Was missing the package sets key from the repo config struct, which
means that the option was being ignored and wasn't being serialised into
the test manifest either.

cmd/gen-manifests/main.go

@@ -46,6 +46,7 @@ type repository struct {
 	RHSM           bool     `json:"rhsm,omitempty"`
 	MetadataExpire string   `json:"metadata_expire,omitempty"`
 	ImageTypeTags  []string `json:"image_type_tags,omitempty"`
+	PackageSets    []string `json:"package-sets,omitempty"`
 }
 
 type ostreeOptions struct {