Support both an internal and external API server endpoint

[nrb]

/kind feature

Describe the solution you'd like

We'd like to use CAPZ within OpenShift, and currently, we support dual endpoints in our clusters. One is external for use with tools like kubectl from user laptops. The other is internal, for traffic between controllers/kubelets and the API server.

It looks like CAPZ already supports an external load balancer for private clusters, but this is egress only. For our use, we would like to create one that also allows ingress.

Anything else you would like to add:

We (Red Hat) would happily take on this work, so long as we know it is acceptable by the maintainers.

[mboersma]

We discussed this at CAPZ office hours and think it would be a big improvement. We'd love to work with your contribution, thanks!