Expose Notifications to allow handler/pipeline override

Getting notifications via email can be a bit overwhelming at times. We would like to be able to plug custom connectors to be able to receive notifications via other communication systems when a job fails or if we start a job to get a notification when it's completed.

We have built a connector for Slack on our side but it's using not recommanded methods, so we would like a legit point of entry to be able to do that.

Thank you.