Newsletter: Sending emails

[elpiel]

Is your feature request related to a problem? Please describe.
Sending the newsletter should be automatic and handled by CI

Describe the solution you'd like
Using lettre crate and the mailchimp account to send emails to all the subscriber of the newsletter.

Describe alternatives you've considered
Sending through mailchimp will require more integration and time to setup, not to mention the added cost for sending emails through their system.

Additional context