fix: dev: Fix OpenSSL 4 compatibility issue when calling X509_get_subject_name()

Starting from OpenSSL 4 the the X509_get_subject_name() function
returns a 'const' pointer to a name instead of a regular pointer.
Duplicate the name before operating on it, then free it.

Closes #5807

Merge branch '5807-openssl-4-X509_get_subject_name-compat-fix' into 'main'

See merge request isc-projects/bind9!11676