CFT: pkgbase support in 15.0

In 2003, freebsd-update arrived, allowing users to perform binary
updates from one FreeBSD release to another.  That's a lot of collective
time and energy saved by freeing regular users from building the same
sources locally.  After a solid 22-year run, freebsd-update support will
end with the 14 branch.  Its successor is pkgbase, which, as the name
suggests, packages FreeBSD's base system.  In short, the base system can
now be managed similarly to third-party packages.  To update from one
point release to another, simply run pkg upgrade.

In late April, key work landed in the main branch to enable fresh
installations of FreeBSD with pkgbase support [0].  Existing systems
running 14.0 or later can also be managed with pkgbase after running
pkgbasify [1], a tool created under sponsorship from the FreeBSD
Foundation to convert existing systems.

We encourage everyone to test pkgbase on spare or test hardware, using
either the installer from one of the latest 15.0 snapshot images [2] or
pkgbasify.  Please note that while most of the preliminary feedback has
been positive, this work is still experimental; you should only test on
systems you can afford to lose and reinstall.

Some outstanding work is planned:
     - FreeBSD handbook documentation
     - Offline installation support (install media packages)
     - Working bootonly.iso
     - Pkgbase-based local and cloud VM images.

The 15.0 release schedule [3] lists the code slush starting on August 8,
so the deadline for this work is only a few months away.  Please test
early and often.  Issues can be reported in Bugzilla using a bug subject
prefixed with 'pkgbase:'

Thanks,
Joe

[0] For now, the installer only offers network pkgbase installs; support
    for installing from optical media or USB images will land soon.
    Also, a known problem with the bootonly.iso will be fixed soon.
[1] https://github.com/FreeBSDFoundation/pkgbasify
[2] https://download.freebsd.org/snapshots/ISO-IMAGES/15.0/
[3] https://www.freebsd.org/releases/15.0R/schedule/