feat: add script to send email digest

[kristovatlas]

This would summarize the total number of domains seen and new ones found over a given period, e.g. a day. This could be run as another cron job, serving the dual purpose of reassuring the recipient that the service is healthy even when not finding new phishing domains.

[0xd34db33f]

Musing as this could help rectify #11 and has database implications from #9 . While we can certainly add a date field to the database entries for found domains, it goes back to the discussion about sanely maintaining it as we discuss in #9. Fine by me though. I think if we add a email digest that should take care of #11 as we can get the ultimate notification we were hoping for.