Add new rc: machine_id to generate /etc/machine-id

This new default-enabled rc will generate a /etc/machine-id file if it
does not exist, and pre-fill it with a newly generated UUID of version 4
[2].

The file is generated in /var/db/machine-id and symlinked to
/etc/machine-id to allow for read-only root partitions.

This file is amongst other things used by libraries like GLib.

Bump FreeBSD version 1400076 to be able to easily add support for older
version of FreeBSD via a package.

[1] Linux machine-id(5): https://www.man7.org/linux/man-pages/man5/machine-id.5.html
[2] f176fe8e7f638e585afcd2f4dd52a522c4648f63

Approved by: bapt
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D37722