When using a custom image for on_exit_notify of a workflow queue and payload should not be mandatory

[afonsobspinto]

When using a custom image for the on_exit_notify I would like to not need to specify the queue and payload parameters since those might not be needed for my custom scenario

https://github.com/MetaCell/cloud-harness/blame/develop/libraries/cloudharness-common/cloudharness/workflows/operations.py#L171