request: Per-channel-user toggle in message spam filter

[kyranet]

Is your feature request related to a problem? Please describe.
The new system tracks messages per-channel, while this avoids chains from happening, it doesn't work very well in certain situations, as well as users can trick others into saying a sentence they repeated multiple times.

Describe the solution you'd like
Add a toggle so they can select between per-channel-user and per-channel, being the former the default behaviour.

Describe alternatives you've considered
Making it per-channel-user instead.

Additional context
None.