main/postmarketos-config-nftables: add rule for ausweisapp2

This solves the pairing between the phone and a laptop when using the local app: https://pkgs.alpinelinux.org/package/edge/community/x86_64/ausweisapp2

However, I wonder if we should enable this port unconditionally, and not with an install_if in a subpackage. The app is in flathub, which is officially supported by the provider, and in fairness I expect most non-technical users to trust it more, due to its sentivity, than whatever a random person (no offense, that could be me) packages in alpine. I don't think opening this high port unconditionally creates any risks, but I'm happy to hear other people's thoughts