FCOS moving iptables to the nft backend

[JaimeMagiera]

This thread is to collate all the information we have on handling FCOS's move of iptables to the nft backend, including the game plan for OKD to support it.

coreos/fedora-coreos-tracker#676

[vrutkovs]

I don't think there's something requires doing - all NFT changes are handled by SDNs. Since RHEL8 (and thus RHCOS) are using NFT by default we'd get NFT support for free