Automation for updates

[Hartmannlight]

I hope we could configure dependabot or something to look for important updates, automaticalle push it to a auto-update branch, run tests and publish it under the auto-update docker tag.
Users can then decide if they want "latest" (manually checked updates), "auto-updates" (with watchtover) or stay on a specific verison.

[Hartmannlight]

I should also review my docker setup in general for best practises (no root user etc.)