We previously fell back to using ClusterIPs. However, the approach can
lead to all kinds of problems since Ingresses rely on being able to talk
to Endpoints directly. For instance, it can break stickiness and
retries.
Instead of doing sanity checks in the Kubernetes provider, we just
accept any non-empty value from the annotation and rely on the server
part to filter out unknown rules.
This allows us to automatically stay in sync with the currently
supported Path matchers/modifiers.
