Email notifications for reviews

**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.