SMPT and brevo backend

[tttp]

we are using swoosh, two to add:

https://hexdocs.pm/swoosh/Swoosh.Adapters.SMTP.html
https://hexdocs.pm/swoosh/Swoosh.Adapters.Brevo.html

to test SMTP, we had great success with https://github.com/mailhog/MailHog as the local server + view of the emails sent
to test brevo, create a free test account

both are about sending messages, what is missing is the return path, so we can be informed if an email wasn't sent.

for smpt, that is not an option.

for brevo, check how it's done for mailjet to handle events, brevo have their own way to handle these webhooks, but conceptually similar