⚠️ Default Kubelet cgroupDriver to systemd for Kubernetes >= 1.21

[fabriziopandini]

What this PR does / why we need it:
back port of #4236

For Kubernetes >= 1.21, image builder is going to setup containerd for using systemd cgroup.
KCP should take care of adapting the Kubelet-Config map to be consistent with this change.

Which issue(s) this PR fixes:
Rif #4099

/area control-plane
/milestone v0.3.x

[neolit123]

technically, the CAPI change is not needed as long as kubeadm init from 1.21 defaults the KubeletConfiguration that it uploads in the cluster to have the systemd driver. if kubeadm is doing that it will match the image-builder driver and i don't see a need for CAPI to do that too?

maybe this code path is done during upgrade, where an old config map has to be migrated to match the image builder driver?

[fabriziopandini]

maybe this code path is done during upgrade, where an old config map has to be migrated to match the image builder driver?

this is the case

WRT to the minor fix, given this is a backport I prefer keep things consistent; eventually we can fix in main and backport those nits well

[vincepri]

/approve
/assign @neolit123
for lgtm

[k8s-ci-robot]

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[vincepri]

/lgtm

[vincepri]

/retest