Link tasks to their restarts

Closes #1711 (closed)

arkindex/ponos/api.py

@@ -224,10 +224,8 @@ class TaskRestart(ProcessACLMixin, CreateAPIView):
                 detail="Task's state must be in a final state to be restarted."
             )
         # TODO Check the original_task_id field directly once it is implemented
-
         # https://gitlab.teklia.com/arkindex/frontend/-/issues/1383
-        _, *suffix = task.slug.rsplit("_old", 1)
-        if suffix:
+        if len(Task.objects.filter(original_task=task)) > 0:
             raise ValidationError(
                 detail="This task has already been restarted"
             )