[Web] allow mailbox authsource to be switchable

data/web/templates/edit/mailbox.twig

@@ -23,8 +23,12 @@
             data-style="btn btn-secondary"
             name="authsource" class="full-width-select form-control" required>
               <option value="mailcow" {% if result.authsource == "mailcow" %}selected{% endif %}>mailcow</option>
+              {% if iam_settings.authsource == 'keycloak' %}
               <option value="keycloak" {% if result.authsource == "keycloak" %}selected{% endif %}>Keycloak</option>
+              {% endif %}
+              {% if iam_settings.authsource == 'generic-oidc' %}
               <option value="generic-oidc" {% if result.authsource == "generic-oidc" %}selected{% endif %}>Generic-OIDC</option>
+              {% endif %}
           </select>
         </div>
       </div>