Slack alert for when there is a new filter rule associated to brave.com domains

[ShivanKaul]

It would be nice to know when an upstream filter list includes *.brave.com (search.brave.com for example) domains.

[ShivanKaul]

This would probably live in https://github.com/brave/adblock-lists-mirror/blob/main/update-lists.py, we would check existing rules and the diff.