Add notifications microservice

[lorenyu]

We recently implemented a self-contained reusable notifications microservice using AWS Pinpoint on an internal project. This ticket is to refine the design (if needed) and bring it over to the template

Scope / Requirements

• Create SES email identity or domain identity
• Create Pinpoint app
• Add instructions for how to spin up microservice and verify email identity or domain identity, and how to test
• Add instructions for how to use this on other apps (e.g. add Pinpoint app id as an env variable to the app and use AWS SDK)

Reference

🔒 Slack thread