Add migration documentation for IngressClass

docs/content/migration/v2.md

@@ -320,3 +320,8 @@ Since `v2.2.5` this rule has been removed, and you should not use it anymore.
 ### File Provider
 
 The file parser has been changed, since v2.3 the unknown options/fields in a dynamic configuration file are treated as errors.
+
+### IngressClass
+
+In `v2.3`, the support of `IngressClass`, which is available since Kubernetes version `1.18`, has been introduced.
+In order to be able to use this new resource the [Kubernetes RBAC](../reference/dynamic-configuration/kubernetes-crd.md#rbac) must be updated. 

docs/content/reference/dynamic-configuration/kubernetes-crd-rbac.yml

@@ -18,6 +18,7 @@ rules:
       - extensions
     resources:
       - ingresses
+      - ingressclasses
     verbs:
       - get
       - list