Support ingress class name in ingress spec

[trennepohl]

What?

• Add standard annotation for specifying the Ingress class name
• Set ingressClassName field in the Ingress Object
• Keep backwards compatibilty with the old annotation
• Always drop kubernetes.io/ingress-class annotation

Why?

• It's prefereable to use the Ingress object attribute instead of the annotation.
• Kubernetes 1.25+ won't support ingressClassName and the annotation kubernetes.io/ingress.class to be set simultaneously