[9.20] new: usr: Add support for multiple extended DNS errors

Extended DNS error mechanism (EDE) may have several errors raised during a DNS resolution. `named` is now able to add up to three EDE codes in a DNS response. In the case of duplicate error codes, only the first one will be part of the DNS response.

Closes #5085

Backport of MR !9952

Merge branch 'backport-5085-multiple-ede-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!9978