Update to new dot release

In order to update to a new release run freebsd-update upgrade.
Get the old version string with file /storage/jails/basejail/bin/sh.

Update jails with ezjail-admin update -U -s 12.3-RELEASE

Update to new patch release

To update the patch version of the host run freebsd-update fetch and freebsd-update install.
Update jails with ezjail-admin update -u