Add cilium_ipam_mode variable (#7418)

Starting with Cilium v1.9 the default ipam mode has changed to "Cluster
Scope". See:

https://docs.cilium.io/en/v1.9/concepts/networking/ipam/

With this ipam mode Cilium handles assigning subnets to nodes to use
for pod ip addresses. The default Kubespray deploy uses the Kube
Controller Manager for this (the --allocate-node-cidrs
kube-controller-manager flag is set). This makes the proper ipam mode
for kubespray using cilium v1.9+ "kubernetes".

Tested with Cilium 1.9.5.

This PR also mounts the cilium-config ConfigMap for this variable
to be read properly.

In the future we can probably remove the kvstore and kvstore-opt
Cilium Operator args since they can be in the ConfigMap. I will tackle
that after this merges.