libknot: add basic support for SVCB and HTTPS records

- They were registered by IANA some time ago:
  https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
- They now appear in traffic quite a lot
  and I'm getting tired of TYPE65 in logs :-)
- I don't expect a more precise descriptor is wanted,
  when comparing to other types.  Wire-format reference:
  https://mikebishop.github.io/dns-alt-svc/draft-ietf-dnsop-svcb-https.html#name-rdata-wire-format
- No displaying or parsing, for now.  (except for displaying the type names)