- Updated the API documentation for Service.Spec.IPFamily to warn that its exact
  semantics will probably change before the dual-stack feature goes GA, and users
  should look at ClusterIP or Endpoints, not IPFamily, to figure out if an existing

- Add dual-stack Services (alpha).  This is a BREAKING CHANGE to an alpha API.
  It changes the dual-stack API wrt Service from a single ipFamily field to 3
  fields: ipFamilyPolicy (SingleStack, PreferDualStack, RequireDualStack),
  ipFamilies (a list of families assigned), and clusterIPs (inclusive of

    * 1. `--service-cluster-ip-range[0]` is consider primary service range, and will be used for any service with `Service.Spec.IPFamily = nil` or any service in the at the time of turning on the feature flag.

- Fixed the EndpointSliceController to correctly create endpoints for IPv6-only pods.
  
  Fixed the EndpointController to allow IPv6 headless services, if the IPv6DualStack
  feature gate is enabled, by specifying `ipFamily: IPv6` on the service. (This already
  worked with the EndpointSliceController.) ([#91399](https://github.com/kubernetes/kubernetes/pull/91399), [@danwinship](https://github.com/danwinship)) [SIG Apps and Network]