Upgrade `k8s.io/kubernetes` dependency

[nikimanoledaki]

https://github.com/weaveworks/eksctl/pull/5604 upgraded the k8s.io/kubernetes dependency from 1.19, which is no longer supported by EKS, to 1.20.

This ticket is to decide if we want to keep the version pinned at all. If we do, then which one?

If we do want to pin it, one option is to keep it the same as eksctl's default k8s version (currently 1.22).

Note

It is not possible to only pin k8s.io/kubernetes as it is not intended to be used that way. If doing this, other k8s.io/xyz subcomponents have to be pinned as well, like this, which is what we do currently: https://github.com/kubernetes/kubernetes/issues/79384#issuecomment-505632294 This script is helpful for doing this for a given k8s version: https://github.com/kubernetes/kubernetes/issues/79384#issuecomment-521493597