new: usr: Add support for EDE 20 (Not Authoritative)

Support was added for EDE codes 20 (Not Authoritative) when client requests recursion (RD) but the server has recursion disabled.

RFC 8914 mention EDE 20 should also be returned if the client doesn't have the RD bit set (and recursion is needed) but it doesn't apply for
BIND as BIND would try to resolve from the "deepest" referral in AUTHORITY section. For example, if the client asks for "www.isc.org/A" but the server only knows the root domain, it will return NOERROR but no answer for "www.isc.og/A", just the list of other servers to ask.

See #1836

Merge branch '1836-not-authoritative' into 'main'

See merge request isc-projects/bind9!10228