Docs and example suggest running aiosmtpd INSECURELY

The authenticated relayed example does NOT actually required authentication to relay.

The docs suggest a similar setup that is INSECURE.

This is a major issue, people will implement their system incorrectly. It will look like it works as using wrong login/password will correctly reject, but using no auth at all will incorrectly accept incoming mail.

This can be fixed for example by checking `session.authenticated` in `handle_RCPT` or `handle_DATA`.