feat(REST): add route-filter alternatives for timeslot endpoint

The nested timeslot routes allowed us to filter the timeslots by show
and schedule. We’ve deprecated nested endpoints with the alpha.2
release, but still need the actual filtering logic.

program/filters.py

@@ -174,6 +174,16 @@ class TimeSlotFilterSet(filters.FilterSet):
         ),
     )
 
+    scheduleIds = IntegerInFilter(
+        field_name="schedule",
+        help_text="Return only timeslots that belong to the specified schedule(s).",
+    )
+
+    showIds = IntegerInFilter(
+        field_name="schedule__show",
+        help_text="Return only timeslots that belong to the specified show(s).",
+    )
+
     def filter_surrounding(self, queryset: QuerySet, name: str, value: datetime.datetime):
         nearest_timeslots_in_future = (
             models.TimeSlot.objects.filter(start__gte=value)