[v9_18] [CVE-2022-3080] Test serve stale cache with timeout 0 and CNAME

Add a couple of tests that verify the serve-stale behavior when stale-answer-client-timeout is set to 0 and a (stale) CNAME record is queried.

Related #3517 (closed)

This was originally https://gitlab.isc.org/isc-private/bind9/-/merge_requests/444