fix: nil: Don't use wildcard keys in update-policy in ddns-confgen

In `ddns-confgen`, if the requested key name is a wildcard, don't generate
an `update-policy` statement, since using a wildcard as an SSU identity
allows other keys that match the wildcard to update records.

Closes #6235

Merge branch '6235-wildcard-ddns-confgen' into 'main'

See merge request isc-projects/bind9!12439