Add option for enabling nested virtualization

### What feature do you want to see added?

Hello team !

We use Android QEMU device for automated tests, and we would like to, instead of using a custom GCE image with the licence key for nested virtualization, simply have a boolean to enable it, to avoid maintaining 2 images nearly identical.

Example :

```yaml
enable_nested_virtualization: true
```

`google compute instances create` command seems to support it :

```
gcloud compute instances create VM_NAME \
--enable-nested-virtualization \
--zone=ZONE \
--min-cpu-platform="Intel Haswell"
```

See [Google doc](https://cloud.google.com/compute/docs/instances/nested-virtualization/enabling).

Thanks and have a good day !

### Upstream changes

_No response_