Document k0s persistence

[kbumsik]

Hi, I am experimenting k0smotron to implement multi-tenant k8s with remote workers.

While playing around k0smotron, one thing I noticed is that documentation on Cluster.spec.persistence is lacking, while it seems to be important for production deployment.

For example:

• What it actually does - the doc doesn't mention what it persists at all. Just saying "persistence configuration" is very confusing. It seems to mount /var/lib/k0s though.
• Recommended size and performance of the volume
  • dose it need to be high-performance? Suggested IOPS? What is the expected size of the volume? Does it keep growing?
  • In case of etcd, it is easier to figure out the optimal pvc settings. However, it is hard to figure out the hardware requirements of k0s control plane instance.
• Maybe also add why it needs a persistent volume. I thought kube-apiserver is stateless.

Since v1 is out, some insights regarding production deployments like this would really helps.