Add opinionated but configurable automatic updates

[cgwalters]

Let's steal some of the logic and code from https://github.com/coreos/zincati/blob/main/docs/usage/auto-updates.md

[lmilbaum]

I'd suggest considering renovatebot as the framework for auto-updating. We can contribute to the project in case it doesn't support this use case.

[anthr76]

Big +1 for renovate. Although I'm not sure how it would work in the model unless a "treefile" is somewhat tracked by GitOps

[LorbusChris]

@lmilbaum as I understand it, this issue is about updating a bootc OS deployment, not about updating code dependencies in this repo. So to me that sounds rather unrelated to renovate.

[LorbusChris]

@cgwalters are you planning on adding support for Cincinnati in bootc, or do you have an alternative in mind?
I think it'd be interesting to investigate ways of distributing the update metadata through OCI registries, instead of through Cinci.

[LorbusChris]

also ref coreos/fedora-coreos-tracker#1263

[cgwalters]

@cgwalters are you planning on adding support for Cincinnati in bootc, or do you have an alternative in mind?

IMO no; that's exactly the kind of thing that can live as a higher level project. A huge difference here vs e.g. FCOS is the emphasis (and raw ability) to trivially derive builds. And one of those things that's now easy to inject is a custom tool to do OS updates.

[cgwalters]

This was fixed by #179