Add ignition to CoreOS version compatibility mappings

[idc77]

Feature Request

Environment

What hardware/cloud provider/hypervisor is being used to run Ignition?

Desired Feature

https://coreos.github.io/ignition/getting-started/
says

One of the most important parts of this config is the version number. This must match the version number accepted by Ignition. If the config version isn’t accepted by Ignition, Ignition will fail to run and the machine will not boot.

Idk if anything else uses ignition, but CoreOS does. In fact, I stumbled upon ignition via CoreOS.

Well, if I use version 3.5.0 on CoreOS 39, I have no idea if it will work , or if I need v3.4.0 or lower.

So, kindly provide supported CoreOS ignition version compatibility.

Other Information

[travier]

You can find what spec is supported by what release in https://coreos.github.io/ignition/specs/#specification-versions-and-ignition-releases and what version of Ignition is included in Fedora CoreOS in https://fedoraproject.org/coreos/release-notes?arch=x86_64&stream=stable.

Does that solve you issue?