Add API endpoint /seats to event (Z#23159536) (#4321)

* add API endpoint /seats to event

* fix logging

* add Seat annotations

* add seats endpoint for subevents

* return ids of occupying objects instead of boolean flags

* wip

* include orderposition instead of order in seat info

* add API documentation

* Apply suggestions from code review

Co-authored-by: Raphael Michel <michel@rami.io>

* Apply suggestions from code review

* Clarify API docs

* add api examples

* add test cases

* require can_view_orders permission for retrieving seats

* improve permission handling

* Revert "improve permission handling"

This reverts commit f32b532cc6.

* improve permission handling (minimal version)

* formatting

* add permission tests

* fix bug

* update permission checks

* Apply suggestions from code review

Co-authored-by: Raphael Michel <michel@rami.io>

* add tests for permission checks

* add tests for expand=voucher and expand=cartposition

* remove unused parameter

* test query count

* codestyle

---------

Co-authored-by: Raphael Michel <michel@rami.io>

src/pretix/base/models/seating.py

@@ -185,7 +185,7 @@ class Seat(models.Model):
 
     @classmethod
     def annotated(cls, qs, event_id, subevent, ignore_voucher_id=None, minimal_distance=0,
-                  ignore_order_id=None, ignore_cart_id=None, distance_only_within_row=False):
+                  ignore_order_id=None, ignore_cart_id=None, distance_only_within_row=False, annotate_ids=False):
         from . import CartPosition, Order, OrderPosition, Voucher
 
         vqs = Voucher.objects.filter(
@@ -214,17 +214,24 @@ class Seat(models.Model):
         )
         if ignore_cart_id:
             cqs = cqs.exclude(cart_id=ignore_cart_id)
-        qs_annotated = qs.annotate(
-            has_order=Exists(
-                opqs
-            ),
-            has_cart=Exists(
-                cqs
-            ),
-            has_voucher=Exists(
-                vqs
+        if annotate_ids:
+            qs_annotated = qs.annotate(
+                orderposition_id=Subquery(opqs.values('id')),
+                cartposition_id=Subquery(cqs.values('id')),
+                voucher_id=Subquery(vqs.values('id')),
+            )
+        else:
+            qs_annotated = qs.annotate(
+                has_order=Exists(
+                    opqs
+                ),
+                has_cart=Exists(
+                    cqs
+                ),
+                has_voucher=Exists(
+                    vqs
+                )
             )
-        )
 
         if minimal_distance > 0:
             # TODO: Is there a more performant implementation on PostgreSQL using