Re-introduce port: devel/mongo-cxx-driver

Official Mongo C++ Driver

Mongo (from "humongous") is a high-performance, open source,
schema-free, document-oriented database. A common name in the
"NOSQL" community.

WWW: https://github.com/mongodb/mongo-cxx-driver

There was an old port, which was not staged.

PR: 195332
Submitted by: numisemis@yahoo.com