Support LoadBalancerClass in Services

[EternalDeiwos]

TL;DR

Following #338; figured posting a new issue was better than thread-necro.

It would be very helpful for CCM to have a loadBalancerClass defined, because I am pretty sure that every other LB implementation out there is going to assume they are the "default". At least Cilium does.

Picking between load balancers is done with the .spec.loadBalancerClass field. When LB IPAM is enabled it allocates and assigns IPs for services with no load balancer class set.

cc @apricote

Expected behavior

I should be able to specify a value for loadBalancerClass to exclude other load balancer implementations.