Disallow unknown fields from resources struct

Before this change, it is possible to passe any additionnal field (in
the yaml/json form) with Tekton resources. This is now disallowed.

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

cmd/webhook/main.go

@@ -97,8 +97,8 @@ func main() {
 			v1alpha1.SchemeGroupVersion.WithKind("TaskRun"):          &v1alpha1.TaskRun{},
 			v1alpha1.SchemeGroupVersion.WithKind("PipelineRun"):      &v1alpha1.PipelineRun{},
 		},
-		Logger: logger,
-
+		Logger:                logger,
+		DisallowUnknownFields: true,
 		// Decorate contexts with the current state of the config.
 		WithContext: func(ctx context.Context) context.Context {
 			return v1alpha1.WithDefaultConfigurationName(store.ToContext(ctx))