Notification on Proc completion

[akshat]

As a user,
I want to be notified when the proc I executed completes.

So that I don't have to pay attention to the progress of procs in execution, and can focus on something else.

Once a proc reaches completion, proctor should notify me about that, and let me know if the proc completed successfully or failed.

Out of scope:
Multiple channels of notification.
For now, proctor will only accept an api during executing a proc. It will notify on that api once the proc reaches completion.
Implement multiple channels for notification later.

[Jenson C S]

Added callback functionality. User Needs to pass callback_url to get job status.