Pod cidrs are not configurable in most ClusterStacks including openstack scs one

[Nils98Ar]

/kind bug

What steps did you take and what happened:

Currently the pod cidrs are not configurable in most ClusterStacks (except the Hetzner one as it seems).

The reason is that by default (ipam mode cluster-pool) cilium uses its own ipam settings for pods and does not respect the Cluster objects .spec.clusterNetwork.pods.cidrBlocks described in the docs:

• cluster-stacks/docs/providers/openstack/quickstart.md

  Lines 203 to 205 in c48b6bc

  	pods:
  	cidrBlocks:
  	- ${CS_POD_CIDR}

• cluster-stacks/docs/providers/openstack/configuration.md

  Lines 17 to 19 in c48b6bc

  	pods:
  	cidrBlocks:
  	- 192.168.0.0/16

We should either switch to ipam mode kubernetes and let cilium use the K8s ipam configuration as in the hetzner ClusterStack or we should make .spec.ipam.podCIDRs in the CiliumNode objects configurable via ClusterClass variable. Propably also configurable via cilium helm value ipam.operator.clusterPoolIPv4PodCIDRList in the ClusterAddon but I think the helm template happens before the ClusterClass templating/patching and therefore we cannot patch helm values this way?

We would also need to check how to deal with existing clusters.