Support pf tables for ipset-like functionality on macOS/FreeBSD

### Problem Description
It would be desirable to be able to run AGH on macOS/FreeBSD and have name resolutions populate `pf` tables for domain-based routing. Specifically, macOS laptop users would benefit from a combined DNS policy and domain-based routing solution while mobile and connecting to different networks without a VPN. FreeBSD users using pfSense, FreeNAS, or the stock distro could also benefit.

### Proposed Solution
Direct connection to `/dev/pf` with ioctls e.g. . I haven't investigated what the situation is on FreeBSD but I reckon it's similar.

### Alternatives Considered
1. Wrap the `pfctl` command line tool. This is probably slow and may be difficult to manage.

### Additional Information
I think the FreeBSD use case is much more compelling than the macOS use case. Perhaps @tejaskokje would be interested?