Delivering reviews over email

Hello,

Sashiko is now able to send reviews over email. It can be configured on
a per-subsystem/mailing-list basis. Sashiko can reply to the author and
cc mailing lists, maintainers and/or listed volunteers.

If you're interested in your subsystem to get email reviews,
please, write into this mailing list or me directly or send a PR changing
this file:
https://github.com/sashiko-dev/sashiko/blob/main/sashiko.dev/email_policy.toml

Please, make sure all maintainers in the subsystem are onboard.

I also have a slight preference to not use reply_all and keep the cc
list relatively short to not pollute all mailing lists.

Thanks!