Email notifications for reviews

[kriswest]

Is your feature request related to a problem? Please describe.
When a user pushes and a review is needed, they currently need to manually notify the reviewers (if any are set-up). When reviews are submitted, the reviewer needs to manually notify the contributor that they have done so. In SCM services (GitHub/GitLab) email notifications are generated for both reviews requested and submitted which reduces the toil in the whole process.

Describe the solution you'd like
Generate email notifications when:

• pushes are submitted for review
• pushes change state (approved, rejected, cancelled).

Support templating or template variables through configuration for emails generated.

Describe alternatives you've considered
Teams integration for notifications.

Additional context
There is some very basic email functionality implemented at: src\service\emailSender.js however it appears to be unused.

[andypols]

I think this should be part of a broader Notifications interface, with different implementations such as email, Teams, or Slack. We can start with a single implementation and allow others to add their preferred channels as needed. Your initial event notifications look good (push state changes and new pushes for review), and we can evolve the functionality over time.