[RFE] Make sure that the sysext-bakery always builds all curent versions of Kubernetes images.

[jhaprins]

Current situation

The sysext-bakery used by Flatcar to create images for Kubernetes is not always up2date with current / maintained versions of Kubernetes.

Impact

This results in having to either build them yourself, or having to stay with older version which could result in security issues.

Ideal future situation

The ideal situation would be that the sysext-bakery would track the releases of Kubernetes and builds new sysext files as soon as a new version of Kubernetes hits the internet.

Implementation options

Track the Kubernetes github releases and build for all maintained releases.

Additional information

[ Please Add any information that does not fit into any of the above sections here ]

[pothos]

In the github action we can fetch the active k8s versions from https://raw.githubusercontent.com/kubernetes/website/main/data/releases/schedule.yaml and filter out releases with a target date in the future (using next: as first try, otherwise the last one from previousPatches)