Implement strongly typed class reconcilers

[n3wscott]

Fixes: #1098

Adding a new annotation config to allow us to configure strongly classed reconcilers, such as Eventing's Broker, or Serving's Ingress.

This will be a breaking API change for types that opt into this behavior. The main changes are the addition of classValue string to NewImpl and NewReconciler (for tests)

NewImpl(ctx context.Context, r Interface, classValue string, optionsFns ...controller.OptionsFn) *controller.Impl

NewReconciler(ctx context.Context, logger *zap.SugaredLogger, client versioned.Interface, lister pubv1alpha1.BarLister, recorder record.EventRecorder, r Interface, classValue string, options ...controller.Options) controller.Reconciler

This feature is enabled with a golang annotation argument:

// +genreconciler:class=example.com/filter.class

[mattmoor]

/lgtm
/approve

[knative-prow-robot]

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This pull-request has been approved by: mattmoor, n3wscott

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