✨(backend) use batches in indexing task

Reduce the number of Find API calls by grouping all the latest changes
for indexation : send all the documents updated or deleted since the
triggering of the task.

Signed-off-by: Fabre Florian <ffabre@hybird.org>

src/backend/core/models.py

@@ -906,7 +906,8 @@ class Document(MP_Node, BaseModel):
 
         # Mark all descendants as soft deleted
         self.get_descendants().filter(ancestors_deleted_at__isnull=True).update(
-            ancestors_deleted_at=self.ancestors_deleted_at
+            ancestors_deleted_at=self.ancestors_deleted_at,
+            updated_at=self.updated_at,
         )
 
     @transaction.atomic