Validation of IngressClass existence can break existing uses of the operator

[dprotaso]

What steps did you take and what happened:

Knative configures two contour instances - one for external and internal traffic. We use ingressClassName as a way to designate between the two instances.

When using this setup with the operator & contour 1.17 it requires us to create an IngressClass object just to satisfy the existence check added by https://github.com/projectcontour/contour-operator/pull/388

What did you expect to happen:

I can create these two contour instances without the need to create an IngressClass object

Anything else you would like to add:

Knative tracking issue: https://github.com/knative-sandbox/net-contour/issues/549

Environment:

• Software version: Contour 1.17
• Kubernetes version: (use kubectl version): any
• Kubernetes installer & version: any
• Cloud provider or hardware configuration: GKE/Kind
• OS (e.g. from /etc/os-release): any

[sunjayBhatia]

Worth noting that Contour standalone (no operator) does not require an IngressClass resource to exist (bc in practice the resource itself is not used for anything, only the name is, and the Ingress spec does not require it to exist when filtering Ingress resources via class name) when configured with the IngressClass name flag so the Operator is adding an additional restriction Contour does not