rdv: add entity to serialize (WIP)

src/Bundle/ChillCalendarBundle/Resources/views/Calendar/newAccompanyingCourse.html.twig

@@ -25,6 +25,7 @@
             chill.displayAlertWhenLeavingUnsubmittedForm('form[name="{{ form.vars.form.vars.name }}"]', 
             '{{ "You are going to leave a page with unsubmitted data. Are you sure you want to leave ?"|trans }}');
         });
+        window.entity = {{ entity_json|json_encode|raw }}; 
     </script>
     {{ encore_entry_script_tags('vue_calendar') }}
 {% endblock %}