Platform: Establish Email Functionality

[brian-montgomery]

The backend will need to email users for the following:

1. Sending the user a receipt of payment.
2. A Magic Link authentication email.
3. Potentially, a password reset (if we implement that)

Unfortunately, Buttondown sends out newsletters, but not individual emails. We'll need to use Sendgrid, Postmark or some similar capability.

Also, take a look at using MJML to provide templating.

[brian-montgomery]

Also, if planning on using Handlebars, look at https://github.com/edus44/mjml-handlebars