This adds three OCI archive format files to the release containing
FreeBSD base images suitable for static linked, dynamic linked and shell
workloads. The shell image also contains pkg-bootstrap and can be easily
extended by installing packages (including pkgbase packages).
Approved by: re (cperciva)
Reviewed by: dch, cpersiva, jlduran, zlei
Differential Revision: https://reviews.freebsd.org/D46759
MFC after: 2 days
(cherry picked from commit d03c82c28da86e0812b98b051d24ae5980804ad7)
(cherry picked from commit 6686056ca3)
