strict decoding error: unknown field "spec.defaultBackendService"

According to the [docs ](https://learn.microsoft.com/en-us/azure/aks/app-routing-nginx-configuration#configuration-of-the-nginx-ingress-controller) I should be able to set the `defaultBackendService` settings, but I am prompted with an error:

`Error from server (BadRequest): error when creating ".\\testnginxcontroller.yml": NginxIngressController in version "v1alpha1" cannot be handled as a NginxIngressController: strict decoding error: unknown field "spec.defaultBackendService"`

I have tried editing the original `Nginxingresscontrollers` and creating my own as a test; neither work.

```yaml
apiVersion: approuting.kubernetes.azure.com/v1alpha1
kind: NginxIngressController
metadata:
name: asdf
spec:
controllerNamePrefix: asdf
ingressClassName: webapprouting.kubernetes.azure.com
loadBalancerAnnotations:
service.beta.kubernetes.io/azure-load-balancer-internal: "true"
defaultBackendService:
name: nginx
namespace: app-routing-system
```

Looking at the schema, this should be possible: https://github.com/Azure/aks-app-routing-operator/blob/main/config/crd/bases/approuting.kubernetes.azure.com_nginxingresscontrollers.yaml

Start by comparing the v1alpha1 CRD in config/crd/bases/approuting.kubernetes.azure.com_nginxingresscontrollers.yaml with the documented defaultBackendService field and the provided testnginxcontroller.yml manifest. Reproduce the strict decoding error, then verify that the manifest is accepted with the intended field and settings.

Written by the indexing model from the issue text.