Set up custom SMTP to enable user sign up with Supabase

[slevin48]

Resend as SMTP provider
https://komododecks.com/recordings/1iFvBhiK1hqJ2XNvDjz7

More resources:
https://github.com/orgs/supabase/discussions/29370
https://supabase.com/docs/guides/auth/auth-hooks/send-email-hook