feat: rename confirmation document to invoice

templates/booking/index.html.twig

@@ -70,10 +70,10 @@
                                 bearbeiten
                             </a>
                         {% endif %}
-                        <a href="{{ path('app_booking_confirmation', { 'id': booking.id }) }}"
+                        <a href="{{ path('app_booking_invoice', { 'id': booking.id }) }}"
                            class="button bg-button button--small"
                            target="_blank">
-                            Bestätigung
+                            Rechnung
                         </a>
                         {% if booking.hasDocuments %}
                             <a href="{{ path('app_booking_documents', { 'id': booking.id }) }}"