Currently our kube_types in the GatewayParameter types follow this pattern:

func (in *Pod) GetExtraVolumeMounts() []corev1.VolumeMount {
	if in == nil {
		return nil
	}
	return in.ExtraVolumeMounts
}

We should move away from this proto-style getters and have a consistent style for the API.

Context: #12117 (comment)