archivers/urbackup-server: update 2.2.11 -> 2.3.7

• Changes some hardcoded paths from /etc/urbackup to ${PREFIX}/etc/urbackup
• Adds a note to UPDATING about the foregoing path change
• Uses sqlite3, lua, and lmdb from ports tree, rather than embedded
• Enables support for mounting of VHD files via fuse

PR: 235432
Submitted by: freebsd@coombscloud.com (maintainer)
Relnotes: https://www.urbackup.org/server_changelog.html