Configurable SVCB _dns.resolver.arpa record to allow DNR for custom DoH

[a7md0]

@robgill

It seems that this request, generalised to the ability to have local SVCB (and HTTPS) records, would probably be better directed upstream to the dnsmasq mailing list, rather than implementing it only for _dns.resolver.arpa. It seems likely that it is a feature that would be implemented at some time in the future as more use is made of these new record types.

Thank you robgill, your documented steps in this topic are exactly what I wanted to achieve DNS delivery of Discovery of Network-designated Resolvers (DNR)