NAT64 Support via af-to

[excavator fidelity]

OPNsense 26.7 is now on FreeBSD 15.1, which means pf now supports the af-to option (manpage).
Currently the only way to perform NAT64 is to use Tayga, but that runs in userspace via TUN.

It would be great if OPNsense would add the ability to configure af-to rules in the OPNsense firewall > NAT page.
That would allow users to migrate off of Tayga and hopefully improve the speed of translation.

Possibly relevant prior discussion: https://forum.opnsense.org/index.php?topic=50096.msg256170#msg256170

[Monviech (Cedrik)]

https://github.com/opnsense/core/issues/10570

[excavator fidelity]

https://github.com/opnsense/core/issues/10570

Thanks! I'll be sure to follow the technical discussion there