release: basic-cloudinit improve default image

• Add the firstboot-freebsd-update package, as long as we do not have pkgbase, this is needed
• Support SLAAC by default to complement DHCPv4 (use SYNCDHP instead)

Signed-off-by: Jose Luis Duran <jlduran@gmail.com>
(cherry picked from commit 120740221fd4a4577e63e6c279f9873cabe449d0)