Release for FreeBSD on AMD64

[michaelquigley]

Add build/release steps for FreeBSD on AMD64.

[michaelquigley]

Related to #603

[qrkourier]

GH Actions doesn't yet have a FreeBSD job runner VM, but it might be possible to cross-compile targeting that OS and at least one architecture, but hopefully amd64 and arm64 both because arm64 is likely to be popular.

For the ziti port I didn't need to do much. There were some things in ziti with OS-specific function defs, so I make FreeBSD duplicates or stubs as appropriate. If zrok doesn't have any internal logic that switches on the OS then there might be nothing at all to port, just build.

[michaelquigley]

If zrok doesn't have any internal logic that switches on the OS then there might be nothing at all to port, just build.

Yes... It's just CGO... There should be nothing to port.