Don't init flags in init()

An issue prevents unit tests to run if flags are initialized in an
init() function. More details there:
golang/go#31859.

A workaround is to init flags another way (here by calling a function
from main()).

main.go

@@ -75,7 +75,7 @@ type apiPackage struct {
 
 func (v *apiPackage) identifier() string { return fmt.Sprintf("%s/%s", v.apiGroup, v.apiVersion) }
 
-func init() {
+func initFlags() {
 	klog.InitFlags(nil)
 	flag.Set("alsologtostderr", "true") // for klog
 	flag.Parse()
@@ -114,6 +114,8 @@ func resolveTemplateDir(dir string) error {
 func main() {
 	defer klog.Flush()
 
+	initFlags()
+
 	f, err := os.Open(*flConfig)
 	if err != nil {
 		klog.Fatalf("failed to open config file: %+v", err)