Add node ranges config in InfrastructureConfig

[defo89]

Summary

Current Shoot .spec.networking.nodes is a string which means only one CIDR can be configured.

However, in on-prem networking there are case where worker nodes reside in different subnets which are not easy to summarise.

We as provider extension can allow configuring array of CIDRs in InfrastructureConfig and update InfrastructureStatusNetworking Nodes field which will be later updated to Shoot status and used as reference e.g. in Calico's IP_AUTODETECTION_METHOD.

[defo89]

Proposal is to follow aws extension approach and add the following to metal Infrastructure:

apiVersion: extensions.gardener.cloud/v1alpha1
kind: Infrastructure
metadata:
  name: infrastructure
  namespace: shoot--foobar--metal
spec:
  providerConfig:
    apiVersion: aws.provider.extensions.gardener.cloud/v1alpha1
    kind: InfrastructureConfig
    networks:
    - name: pod-a
      workers: 10.250.10.0/24
      vlan: 500
    - name: pod-b
      workers: 10.250.11.0/24
      vlan: 501

This will:

• today: update ranges in Infrastructure.status.networking.nodes, so that is copied to Shoot.status.networking.nodes.
• later: trigger some network API to provision required networks.

These networks could also be referenced in WorkerConfig to signal that worker pool needs IP assignment from respective IP address pool.