Add option to configure machine config pools

[glrf]

Checklist

• PR contains a single logical change (to build a better changelog).
• Update the documentation.
• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog.

[glrf]

I will add a how to explaining some of the ways to use machine pool configs and some pitfalls in a separate PR. But I'd like to have a general review of the component first.

Also this change will most likely cause all worker nodes to reboot one after another as OpenShift somehow doesn't understand that the machine config did not actually change. Should we mark this as breaking, as this should be released during a maintenance window?

[bastjan]

LGTM, with the std.prune addressed as discussed.

[simu]

LGTM overall, take or leave the suggestions on how we could reduce code duplication, it's not that problematic here.

Generally speaking, I feel like the implementation for containerruntimeconfigs and kubeletconfigs is just cryptic enough that it would greatly benefit from short comments explaining what's happening. As it is, it took me a while to figure out what the code is doing (I actually read the parameter docs before going back to reviewing the code)

[glrf]

Did a bunch of refactoring and removed some magic. I hope this is no a bit more readable.

[simu]

This requires Jsonnet 0.18.0, which is probably fine at this point (at least my local Commodore install has Jsonnet 0.18.0)

[simu]

Also this change will most likely cause all worker nodes to reboot one after another as OpenShift somehow doesn't understand that the machine config did not actually change. Should we mark this as breaking, as this should be released during a maintenance window?

I think I'm in favor of making this a new major version, to clearly signal that it needs special care (and to ensure Renovate doesn't auto-update the VSHN defaults)