sysutils/simplesnap: Add new port

simplesnap is a powerful system for transferring ZFS snapshots across
a network. Although it can serve many purposes, its primary goal is to
manage backups from one ZFS filesystem to a backup filesystem also
running ZFS, using incremental backups to minimize network traffic and
disk usage.

WWW: https://github.com/jgoerzen/simplesnap

PR: 280330