Enhancement: Notifications Cache

[domwhewell-sage]

Description
It would be nice for BBOT 2.0 if a notifications cache feature was available. The current notifications modules Discord / Slack / Teams will ping as soon as the event_type is discovered which is a great feature! However for named scans that run on a regular basis the pinging of these services can get overwhelming and interesting new finds can get buried.

This could be implemented with the notifications output modules performing some checks on when this event was last seen before emitting it. The cache should have an expiry time also.