Make email credentials optional

[ali-beep]

It looks like SMTP credentials are currently required to email tokens. My local SMTP server does not have AUTH enabled. It looks like I have no option between going into the logs to retrieve tokens, or setting up AUTH on my SMTP server. It would be great if bencher could simply not use AUTH if there are no configured credentials.

[epompeii]

@ali-beep thank you for using Bencher, and I'm sorry the current feature set does line up with your use case.

If you would like to make SMTP credentials optional, this is something that I would be open to a PR for. The key change would be here:

bencher/lib/bencher_schema/src/context/messenger/email.rs

Line 119 in 54d78b9

.credentials((self.username.clone(), String::from(self.secret.clone())))

Let me know if you have any questions before you dive in!