Items: Allow plugins to put forms above a formset (#5460)

src/pretix/control/signals.py

@@ -310,9 +310,13 @@ an instance of a form class that you bind yourself when appropriate. Your form w
 as part of the standard validation and rendering cycle and rendered using default bootstrap
 styles. It is advisable to set a prefix for your form to avoid clashes with other plugins.
 
-Your forms may also have two special properties: ``template`` with a template that will be
-included to render the form, and ``title``, which will be used as a headline. Your template
-will be passed a ``form`` variable with your form.
+Your forms may also have special properties:
+
+- ``template`` with a template that will be included to render the form. Your template will be passed a ``form``
+  variable with your form.
+- ``title``, which will be used as a headline.
+- ``ìs_layouts = True``, if your form should be grouped with the ticket layout settings (mutually exclusive with setting ``title``).
+- ``group_with_formset = True``, if your form should be grouped with a formset of the same ``title``
 
 As with all event plugin signals, the ``sender`` keyword argument will contain the event.
 """