Newsletter: Sending emails

**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**