Update to CoreOS ignition specification v3.4.0

[Gerrit91]

We are actually transpiling ignition user data with the os-metal-extension with version 2.3.0.

Upstream there is already v3.4.0 available: https://coreos.github.io/ignition/specs/

In order to allow the migration and do not break existing images, we need to find a solution. For instance, we could programmatically run the ignition executor through the metal-hammer in the chroot of the os image. This way we would decouple the ignition binary installed on the images from our provisioning procedure.

[robertvolkmann]

Are there any plans to remove Ignition and rely solely on Cloud-init, which has been included in the images for several years?

[majst01]

I would like to stay with ignition, but as this issue states, with the newer spec

[robertvolkmann]

Cluster API only supports ignition v2 and no one is maintaining it. Additional, cloud-init is not working anymore in our images, see comments in #272.