sysutils/cpdup-FreeBSD: Add FreeBSD fork of cpdup

Add a fork of cpdup, including patches to support copy_file_range(2)
and allowing to choose checksum algorithm.

Thanks to mm for providing the required patches to the fork.

Assign port to cpdup maintainer

Approved by: Gianmarco Giovannelli <gmarco@giovannelli.it> (maintainer)