mail/goimapnotify: Add new port

Execute scripts on IMAP mailbox changes
(new/deleted/updated messages) using IDLE.
WWW: https://gitlab.com/shackra/goimapnotify

PR: 290048
Reported by: Denis Shaposhnikov <dsh@bamus.cz>
Co-authored-by: Julian Weigt <juw@posteo.de>
Approved by: osa (mentor)