Remove support for `extensions/v1beta1/Ingress` and "networking.k8s.io/v1beta1/Ingress"

Summary

#2852 (closed) requires Kubernetes 1.19 or newer. This version requirement means that networking.k8s.io/v1/Ingress will be available in all supported versions. As a result, we can adjust the ingress API version template and pin to networking.k8s.io/v1/Ingress.

Depending on when this is addressed, we can skip past #2981 (closed).

Acceptance criteria

• Ingress API template pins to networking.k8s.io/v1/Ingress
• All references to older Ingress versions are removed