Add ability to forbid email addresses with user-specified expressions #651

What's the problem this feature will solve?

Some projects, like FreeBSD, do not accept commits from anonymous authors, such as jane.doe@users.noreply.github.com [1]. This is because GitHub author usernames can be changed [2], breaking the account email provided by GitHub.

Describe the solution you'd like

• Being able to specify a regex (in the vein of author-email) which forbids certain email domains/patterns is desirable, for flexibility reasons.
• Having a way to forbid GitHub email addresses using a boolean toggle would be a nice bonus, but it's not a requirement.

Additional context

1. https://docs.github.com/en/account-and-profile/how-tos/email-preferences/setting-your-commit-email-address#setting-your-commit-email-address-on-github
2. https://docs.github.com/en/account-and-profile/how-tos/account-management/changing-your-username