Enable ability to customize the notification that is triggered during a Box Relay workflow.

E.g. if an approval task is approved, I want to notify whoever submitted the content for approval AND potentially other relevant parties that their submission was approved, but I also want to potentially customize the notification (e.g. it was approved for x, y, and z reasons).

E.g. if an approval task is denied, I want to notify whoever submitted the content for approval AND potentially other relevant parties that their submission was denied, but I also want to potentially customize the notification (e.g. it was denied for x, y, and z reasons).