feat: Refactor provisioning to instance requests and enhance subdomain availability check

Website/templates/admin_invoices.html

@@ -64,7 +64,7 @@
         {% endfor %}
         
         {% if provision_requests %}
-        <h2>Provisionierungsanfragen</h2>
+        <h2>Instanz-Anfragen</h2>
         {% for prov in provision_requests %}
         <article class="entry">
             <h3>{{ prov.booking_number or prov.booking_number }}</h3>
@@ -105,7 +105,7 @@
                 <button type="submit">Konfiguration ausführen</button>
             </form>
             <form method="post" style="display:inline-block; margin-right:0.6rem;">
-                <input type="hidden" name="action" value="delete_provision">
+                <input type="hidden" name="action" value="delete_instance_request">
                 <input type="hidden" name="prov_id" value="{{ prov.id }}">
                 <button type="submit" class="danger">Löschen</button>
             </form>