fix(api): replace the build of the ids of documents by a single SQL query.

This increases the performance of `/api/documents/` up to 60% on a ~1400 documents database (~600 ms > ~240 ms on laptop). This optimization only applies to the basic "list documents case", not the "search case".

src/paperless/views.py

@@ -56,11 +56,7 @@ class StandardPagination(PageNumberPagination):
                     except Exception:
                         pass
         else:
-            for obj in self.page.paginator.object_list:
-                if hasattr(obj, "id"):
-                    ids.append(obj.id)
-                elif hasattr(obj, "fields"):
-                    ids.append(obj.fields()["id"])
+            ids = self.page.paginator.object_list.values_list("pk", flat=True)
         return ids
 
     def get_paginated_response_schema(self, schema):