[9.20] fix: dev: Split and simplify the use of EDE list implementation

Instead of mixing the dns_resolver and dns_validator units directly with
the EDE code, split-out the dns_ede functionality into own separate
compilation unit and hide the implementation details behind abstraction.

Additionally, the new dns_edelist_t doesn't have to be copied into all
responses as those are attached to the fetch context, but it could be
only passed by reference.

This makes the dns_ede implementation simpler to use, although sligtly
more complicated on the inside.

Closes #5141

Backport of MR !10016

Merge branch 'backport-5141-ede-mem-fix-v2-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10030