This allows kube-controller-manager to allocate CIDRs to nodes (with
allocate-node-cidrs=true), but will not try to configure them on the
cloud provider, even if the cloud provider supports Routes.

The default is configure-cloud-routes=true, and it will only try to
configure routes if allocate-node-cidrs is also configured, so the
default behaviour is unchanged.

This is useful because on AWS the cloud provider configures routes by
setting up VPC routing table entries, but there is a limit of 50
entries.  So setting configure-cloud-routes on AWS would allow us to
continue to allocate node CIDRs as today, but replace the VPC
route-table mechanism with something not limited to 50 nodes.

We can't just turn off the cloud-provider entirely because it also
controls other things - node discovery, load balancer creation etc.

Fix #25602