Add feature to optionally get callback from user for deploy.

[fristonio]

Since the deployment for the demo is done asynchronously the deployer is sent a response stating deployment has started. So as of now, user don't get notified whether the demo has been deployed or not. As a solution to this, we can optionally ask deployer for the callback URI, which we will make a ping request to once the demo is deployed, this will notify the user that demo has been deployed and is ready for use.