add feedback when moving reservation slot

reservation/templates/reservation/schedule.jinja

@@ -13,6 +13,14 @@
 
 {% block content %}
   <h2 class="margin-bottom">{% trans %}Room reservation{% endtrans %}</h2>
+  <p
+    x-data="scheduleMessages"
+    class="alert snackbar"
+    :class="alertMessage.success ? 'alert-green' : 'alert-red'"
+    x-show="alertMessage.open"
+    x-transition.duration.500ms
+    x-text="alertMessage.content"
+  ></p>
   <room-scheduler
     locale="{{ LANGUAGE_CODE }}"
     can_edit_slot="{{ user.has_perm("reservation.change_reservationslot") }}"