Create subnets in all zones

[sagikazarmark]

Is your feature request related to a problem? Please describe. Node pools can be spread across several subnets/zones in a cluster, but we only create one at the moment.

Describe the solution you'd like to see Create a subnet for all chosen zones.

Additional context Only one zone can be chosen per node pool.

Todos

• [ ] Document that zone determined by the subnet takes precedence over node pool zone