Support skip information reconfirm when using external IDP

Signed-off-by: hongming <hongming@kubesphere.io>

pkg/controller/user/user_webhook.go

@@ -58,6 +58,10 @@ func (a *EmailValidator) Handle(ctx context.Context, req admission.Request) admi
 }
 
 func emailAlreadyExist(users v1alpha2.UserList, user *v1alpha2.User) bool {
+	// empty email is allowed
+	if user.Spec.Email == "" {
+		return false
+	}
 	for _, exist := range users.Items {
 		if exist.Spec.Email == user.Spec.Email && exist.Name != user.Name {
 			return true