add ingress class support

[M00nF1sh]

Add ingress class support

This change will add Ingress class support, the only supported field in IngressClass is the controller field. In the future, we'll leverage the parameters field for more customizations.

Behavior

• If only kubernete.io/ingress.class annotations presents, we consider IngressClass matches this controller if

  • when --ingress-class is specified with non-empty value, and it matches annotation value (when install via YAML/Helm, by default it's specified as alb):
  • when --ingress-class is specified with empty value, and annotation value is empty or alb.

• If only spec.ingressClassName non-nil, we consider IngressClass matches this controller if

  • the corresponding IngressClass exists and the spec.controller of IngressClass have value ingress.k8s.aws/alb

• If both kubernete.io/ingress.class annotation presents and spec.ingressClassName non-nil, we will favor kubernete.io/ingress.class and issue a warning event to Ingress if match result conflicts.
  we do this to align with IngressSpec's recommendation:For backwards compatibility, when that annotation is set, it must be given precedence over this field. The controller may emit a warning if the field and annotation have different values.

• If neither kubernete.io/ingress.class annotation presents and spec.ingressClassName non-nil, we consider IngressClass matches this controller if --ingress-class is specified with empty value

Future plans

1. we'll offer an option to disable kubernete.io/ingress.class annotation support in future versions with default value false in future versions. (this will help us enforce permission control via IngressClass)
2. we'll change the option above to have default value true post X versions.
3. we'll remove the code that support kubernete.io/ingress.class post Y versions.
4. IngressClass's parameters will only be respected if IngressClass is decided from spec.ingressClassName. (i.e. kubernete.io/ingress.class annotation absents)

Note to reviewer:

1. I'll have follow up PR to add RBAC permissions
2. I'll have follow up PR to adjust the behavior of decide whether Ingress should be groupMember if there are errors like ingressClassName not found.

[k8s-ci-robot]

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This pull-request has been approved by: kishorj, M00nF1sh
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