[Bug Report]: Hostpool API no longer returns registratrionInfo

### Describe the bug

I am using the AVD-Accelerator templates, but was trying to upgrade the HostPool API version because the version they use doesn't support the startVMOnConnect setting.

When I upgrade to the latest version, it no longer returns registrationInfo which is being used as an output and the auto generated token is passed to the extension that joings the VM to the HostPool.

The documentation that I can find is pretty scarce on how to use registrationInfo now. What is the suggested method for creating a HostPool and assigning a VM to it now?

https://github.com/Azure/avdaccelerator/issues/330

### To reproduce

Run AVD-Accelerator templates but upgrade the hostpool to use the latest API.

### Code snippet

_No response_

### Relevant log output

```
{
"status": "Failed",
"error": {
"code": "DeploymentOutputEvaluationFailed",
"message": "Unable to evaluate template outputs: 'hostPoolRegistrationInfo'. Please see error details and deployment operations. Please see https://aka.ms/arm-common-errors for usage details.",
"details": [
{
"code": "DeploymentOutputEvaluationFailed",
"target": "hostPoolRegistrationInfo",
"message": "The template output 'hostPoolRegistrationInfo' is not valid: Template parameter 'hostPoolRegistrationInfo' was provided an invalid value. Expected a value of type 'Object', but received a value of type 'Null'. Please see https://aka.ms/arm-create-parameter-file for usage details.."
}
]
}
}
```