security/py-pnu-vuxml: New port: FreeBSD VuXML library and query tool

• Submitter becomes maintainer

pnu-vuxml is both a Python command-line tool and a library that can be
used to query or process the FreeBSD VuXML "database" of vulnerable
ports, making it much more user-friendly and useful.

(Dependency of upcomming Port Tree Linter port)

PR: 277766