Implement Extended DNS Errors - RFC 8914

[aeden]

RFC 8914 defines extended error codes: https://tools.ietf.org/html/rfc8914 - it would be useful to support these in erldns.

[weppos]

• Bind 9 supports it
• PowerDNS authoritative doesn't support it, only recursor
• NSD supports it
• CF 1.1.1.1 resolver supports it