API: Allow to filter quota list for multiple subevents

doc/api/resources/quotas.rst

@@ -89,7 +89,8 @@ Endpoints
    :query integer page: The page number in case of a multi-page result set, default is 1
    :query string ordering: Manually set the ordering of results. Valid fields to be used are ``id`` and ``position``.
                            Default: ``position``
-   :query integer subevent: Only return quotas of the sub-event with the given ID
+   :query integer subevent: Only return quotas of the sub-event with the given ID. Can be passed multiple times to filter
+                            for multiple sub-events.
    :query string with_availability: Set to ``true`` to get availability information. Can lead to increased answer times.
    :param organizer: The ``slug`` field of the organizer to fetch
    :param event: The ``slug`` field of the event to fetch

src/pretix/api/views/item.py

@@ -52,7 +52,7 @@ from pretix.api.serializers.item import (
 from pretix.api.views import ConditionalListView
 from pretix.base.models import (
     CartPosition, Item, ItemAddOn, ItemBundle, ItemCategory, ItemVariation,
-    Question, QuestionOption, Quota,
+    Question, QuestionOption, Quota, SubEvent,
 )
 from pretix.base.services.quotas import QuotaAvailability
 from pretix.helpers.dicts import merge_dicts
@@ -459,6 +459,8 @@ class QuestionOptionViewSet(viewsets.ModelViewSet):
 
 with scopes_disabled():
     class QuotaFilter(FilterSet):
+        subevent = django_filters.ModelMultipleChoiceFilter(queryset=SubEvent.objects.all())
+
         class Meta:
             model = Quota
             fields = ['subevent']