template://k8s: support multi-node mode (w/ `.param`)

[AkihiroSuda]

[...]

#2633

Slightly off-topic here, but we should be able to extend the upstream k8s.yaml to include what was proposed in #2633.

• Flannel can be unconditionally enabled even for a single-node cluster
• vmnet (or user-v2, in case of non-macOS) should be specified via limactl create --network
• Port forwards can be disabled via --set. We may also consider having --port-forward-none as an alias of it
• The PR does not seem to have kubeadm join, but it can be supported with .param that distinguish the worker nodes from the control planes

Originally posted by @AkihiroSuda in #4097

[nirs]

This is not about multiple nodes but multiple clusters, but multiple nodes is another case when real ip address will help.

But making the existing template configurable may be a better way than adding another template.

[afbjorklund]

Previous issue about multi-node clusters:

• Multi-node kubernetes clusters #1184