Allow custom service annotations

Some cloud providers, such as Azure, can have strciter organizational policies where load balancers cannot be used with public IPs.
To avoid this default behavior, users can annotate their LoadBalancer services with azure-load-balancer-internal so that it is not exposed to the internet - https://docs.microsoft.com/en-us/azure/aks/internal-lb.

I'm not suggesting that we try and add support for all of the little quirks of each platform, however we should at least allow users to specify custom annotations to apply to their services to be flexible for different kinds of deployment.