kubeadm's v1beta4 API

[Lubomir I. Ivanov]

with the 1.31 release of k8s, kubeadm will release a new version of
its configuration API - v1beta4. this API took us more than 2 release
to prepare. after that we will be focusing on the future v1.

the work is already merged in master (1.31 pre) and we have unit and
e2e tests running on it, plus we did some manual testing, of course.

if you can give us some early feedback it would be appreciated!
remember that you can build kubeadm from kubernetes/kubernetes with
"make all WHAT=cmd/kubeadm" and the resulted binary will be in
"./_output", then when creating a cluster you can use an older
"kubernetesVersion: 1.30" too.

list of changes since v1beta3:
https://github.com/kubernetes/kubernetes/blob/master/cmd/kubeadm/app/apis/kubeadm/v1beta4/doc.go#L25

from the release note:
--------------
The API does include a few breaking changes:
- The "extraArgs" component construct is now a list of "name"/"value"
pairs instead of a string/string map. This has been done to support
duplicate args where needed.
- The "JoinConfiguration.discovery.timeout" field has been replaced by
"JoinConfiguration.timeouts.discovery".
- The "ClusterConfiguration.timeoutForControlPlane" field has been
replaced by "{Init|Join}Configuration.timeouts.controlPlaneComponentHealthCheck".
Please use the command "kubeadm config migrate" to migrate your
existing v1beta3 configuration to v1beta4.

v1beta3 is now marked as deprecated but will continue to be supported
until version 1.34 or later.
The storage configuration in the kube-system/kubeadm-config ConfigMap
is now a v1beta4 ClusterConfiguration.
--------------

tickets of reference:
https://github.com/kubernetes/kubernetes/pull/125029
https://github.com/kubernetes/kubeadm/issues/2890

thanks
lubomir
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