[occm]Allow the service support customize load-blancer

[A10ss]

/kind feature

What happened:
We have some requirements about setup a customize load-blancer for service. Cloud we add a annotation that let service could use the customize load-blancer or we already have one?

What you expected to happen:
If we could add an annotation to service such as:

annotations:
    loadbalancer.openstack.org/customized-load-balancer-id=xxxx

And then we could add some logic for OCCM and let it use this annotation's load-blancer id to setup the customize load-blancer.