This could be run as a cron job on any Debian based system (tested on Debian, Ubuntu, Raspian).
#!/bin/bash
export DEBIAN_FRONTEND=noninteractive
yes '' | apt-get -y -o DPkg::options::="--force-confdef" -o DPkg::options::="--force-confold" dist-upgrade
See http://slave27.local/debian-handbook/sect.automatic-upgrades.html for more details.