Select different email address to receive notifications, per project

Problem to solve

The work in https://gitlab.com/gitlab-org/gitlab-ce/issues/8111#note_207517879 added group-level email routing, but we still dont have routing per project. We should provide a way to specify which email to use on a per-project basis

Intended users

Further details

Proposal

Add project-level email routing to Profile notification settings

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references