feat: groups price calculator admin crud, booking/offer flow and api

templates/admin/additional_service/create.html.twig

@@ -0,0 +1,6 @@
+{% extends 'layout_admin.html.twig' %}
+
+{% block content %}
+    <twig:page:heading>Zusatzleistung neu für Gruppenhaus {{ accommodation.name }}</twig:page:heading>
+    {% include 'admin/additional_service/_form.html.twig' %}
+{% endblock %}