Send confirmation emails
An email with confirmation code/link should be sent to users that enter their email address.
The link should direkt to a page, that moves the email address from unconfirmed to confirmed.
Possible rust packages to use:
Caution: https://users.rust-lang.org/t/rust-sendmail-security-vulnerabilities-how-to-handle-it/18898
Could be added as a crate feature