Maybe you'll find dockcheck is a more mature and rounded version of what you wanted, and you can fork it to tinker with the other features you want for your own personal use if it doesn't do everything you wanted! Or maybe you'll find you like yours better anyway. Hope you find something interesting in it, regardless!
I personally find dockcheck on each host + a simple systemd service is more or less perfect for my needs. I hook it up to a grafana dashboard so it can give me a running tally of what's out of date and what's not alongside the rest of my monitoring stack.