Success confirmation feature

[jonparker]

Add a feature that allows for the endpoint to call back to the webhook on some URL to notify that the job or workload has completed. This would enable more analytics of how much carbon emissions were saved by the Green Webhook moving the workload.

Note that this wouldn't give an actual Kg of CO2 measurement as it would take much more work to know how many Killowatts of power the workload consumed.