Document spec.network more elaborately

[franpog859]

Is your feature request related to a problem? Please describe.

I don't know what spec.network.serviceCIDR does when I use Calico. I don't know what the spec.network.calico.mode, spec.network.calico. overlay do based on the documentation. I don't know the version of Calico used in the k0s. Does k0s use the chart-based Calico deployment or some custom-made manifests

Describe the solution you would like

It'd be great to have all of it described or at least linked to a Calico (or other) documentation

Describe alternatives you've considered

I dug through the code and experimented with deploying different configurations. It took quite some time

Additional context

No response