Create upgrade script for pulling and upgrading container images

[802compute]

This shell script partially solves the proposed idea #7 to perform an upgrade of the Pi-Hole and Internet-monitoring containers. This does not cover the backing up of any configuration files, though after running this upgrade a few times in my Pi-Hole instance didn't show any loss of configuration files for Grafana, Prometheus or Pi-Hole.

[geerlingguy]

My plan is to have this run as another Ansible playbook—most likely... though I might be okay with going with a shell script as long as it remains nice and simple. For now I'll just leave this open as 'planned' though, so I have more time to think about it.