wip: guest account registration (self-service and booking create flow)

templates/booking/create/step_4.html.twig

@@ -486,6 +486,11 @@
                                     'label_attr': {'class': 'text-base font-semibold'}
                                 }) }}
                             {% endif %}
+                            {% if form.guestAccountOptIn is defined %}
+                                {{ form_row(form.guestAccountOptIn, {
+                                    'label_attr': {'class': 'text-base font-semibold'}
+                                }) }}
+                            {% endif %}
                             {{ form_row(form.confirmationAccepted, {
                                 'label_attr': {'class': 'text-base font-semibold'}
                             }) }}