Order-level questions (#6471)

* New CheckoutSession model, created and deleted throught cart lifetime but only used for order-level question answers so far
* Order-level QuestionAnswers (relations to CheckoutSession / Order)
* New container_type field on Question model to specify whether Question belongs to order or orderposition
* Order-level questions are currently experimental, UI is hidden behind feature flag

---------

Co-authored-by: Richard Schreiber <schreiber@pretix.eu>

src/pretix/api/serializers/item.py

@@ -619,7 +619,7 @@ class QuestionSerializer(I18nAwareModelSerializer):
         options_data = validated_data.pop('options') if 'options' in validated_data else []
         items = validated_data.pop('items', [])
 
-        question = Question.objects.create(**validated_data)
+        question = Question.objects.create(**validated_data, container_type=Question.ContainerType.ORDERPOSITION)
         question.items.set(items)
         for opt_data in options_data:
             QuestionOption.objects.create(question=question, **opt_data)

src/pretix/api/views/item.py

@@ -475,7 +475,10 @@ class QuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
     write_permission = 'event.items:write'
 
     def get_queryset(self):
-        return self.request.event.questions.prefetch_related('options').all()
+        return self.request.event.questions.filter(
+            # the container_type parameter is undocumented, this API is going to change in a later release
+            container_type=self.request.GET.get('container_type', Question.ContainerType.ORDERPOSITION),
+        ).prefetch_related('options').all()
 
     @transaction.atomic()
     def perform_create(self, serializer):