Add a periodic task to reap unreleased receptor work units

- Add work_unit_id field to UnifiedJob

awx/api/serializers.py

@@ -768,6 +768,7 @@ class UnifiedJobSerializer(BaseSerializer):
             'result_traceback',
             'event_processing_finished',
             'launched_by',
+            'work_unit_id',
         )
 
         extra_kwargs = {