[Feature Request] Filter forwarded traffic

### Summary:

OpenSnitch works quite well testing host-based firewalls. I currently have setup where `opensnitchd` runs on the client device, and `opensnitch-ui` is run on the "router".

However, it would be useful to just run both `opensnitchd` and `opensnitch-ui` on the router, and have it filter the traffic of multiple client device on a LAN with the same ruleset.

Would this be out of scope for the project?

Start by reviewing the opensnitchd and opensnitch-ui architecture and how traffic filtering and rules are handled. The issue does not name files or tests; determine whether router-side filtering for multiple LAN clients with one ruleset is supported, and define the tests and behavior that would demonstrate completion.

Written by the indexing model from the issue text.