Deprecate top level Kubelet and Container Runtime configs

[glrf]

Context

In #50 we introduced the option to manage machine config pools. We also added the option to specify KubeletConfig and ContainerRuntimeConfig as part of the machine config pool parameter.

There is always a 1:1 mapping from container runtime and kubelet config to machine config pool.

We should deprecate the top level kubeletConfigs and containerRuntimeConfigs parameters, as specifying them trough the machine config pool is sufficient and more convenient. We also need to document how to move to the new way of configuring things.

Create follow up to have it finally removed.

Alternatives

Keep two ways of defining KubeletConfig and ContainerRuntimeConfig resources