Replace the kubernetes.io/ingress.class annotation with the ingressClassName field

Use the ingressClassName field instead of the kubernetes.io/ingress.class annotation in Ingress resources.

https://kubernetes.io/docs/concepts/services-networking/ingress/#deprecated-annotation

addon/thanos/templates/ingress-prometheus.yaml

@@ -2,11 +2,11 @@ apiVersion: networking.k8s.io/v1
 kind: Ingress
 metadata:
   annotations:
-    kubernetes.io/ingress.class: traefik
     traefik.frontend.entryPoints: http
   name: prometheus
   namespace: kube-system
 spec:
+  ingressClassName: cern-magnum-traefik
   rules:
   - host: {{ .Values.clusterName }}-prometheus.cern.ch
     http: