Allow configuration of Pod CIDR Range

[lfrancke]

We don't use it but Krustlet defaults to use one.
We need to disable it to not cause issues:

• range_allocator.go crashes the entire KCM if CIDRs are incorrect for a single node kubernetes/kubernetes#95948
• Mechanism to specify Krustlet's Pod CIDR? krustlet/krustlet#252

[lfrancke]

It seems as if setting the value to an empty strings works and allows the apiserver to assign a valid range.