fix: dev: Fix delegdb dump buffer overflow

A buffer used to dump a DNS name in the delegdb dump flow was using the
wrong size: it was using `DNS_NAME_MAXWIRE` which is the actual max
length of a DNS name on the wire instead of using `DNS_NAME_FORMATSIZE`
which is the maximum length of a textual representation of a DNS name
(which can be way longer than `DNS_NAME_MAXWIRE` if using the master
file escape sequence format) plus 1 (end of string byte). This could
lead to a buffer overflow. This is now fixed.

Closes #6132

Merge branch '6132-delegdb-dump-overflow' into 'main'

See merge request isc-projects/bind9!12195