Feature request: support Network-designated Resolvers (DNR) as per RfC 9463


RfC 9463 https://datatracker.ietf.org/doc/rfc9463/ introduces in section 6 a new RA option for Encrypted DNS.

It would be great if radvd could support this feature.

I would also see a convinience inhaving  this dynamic as for the RDNSS feature request in #126 when the rsolver runs on the same machine as radvd.

Thanks for considering. 