LoadBalancer IPAM: support IP assignment with `Service.spec.externalIPs/loadBalancerIP`

We use Calico for BGP peering and announcing Service IPs to the upstream fabric.

BGPConfiguration allows Services from pre-defined ranges to be used and announced:

› kubectl get bgpconfiguration default -oyaml | yq .spec.serviceLoadBalancerIPs
- cidr: 10.10.10.0/24
- cidr: 192.168.0.0/27

It would be great if Loadbalancer controller would not only tolerate projectcalico.org/loadBalancerIPs for manual assignment but also actual Service.spec.externalIPs and Service.spec.loadBalancerIP.

This would help to gradually migrate existing charts when payload is deployed to clusters where Calico LoadBalancer IP address management is used without having to switch the whole chart fleet to the Calico-specific annotation.