NotificationHubs Namespace NamespaceType not Returned in Response

Hi, the `namespaceType` property in notificationhubs namespace seems to be missing starting from some time around 2021/12/06.
https://github.com/Azure/azure-rest-api-specs/blob/577c0349bc704c998a662843446347d315098dab/specification/notificationhubs/resource-manager/Microsoft.NotificationHubs/stable/2017-04-01/notificationhubs.json#L1679-L1685
The test we ran at 2021/12/03 still had it in the response.

Test I've made today using REST API (sensitive info removed):
I tried setting `namespaceType` to `Messaging` and `NotificationHub`, both are not shown in the GET response.
```
PUT https://management.azure.com/subscriptions//resourceGroups//providers/Microsoft.NotificationHubs/namespaces/?api-version=2017-04-01
{
"sku": {
"name": "Free"
},
"properties": {
"enabled": true,
"namespaceType":"Messaging"
},
"location": "East US",
"tags": {
"env": "Test"
}
}

GET response body:
{
"sku": {
"name": "Free"
},
"properties": {
"provisioningState": "Succeeded",
"status": "Active",
"createdAt": "2022-01-07T02:46:28.9200000Z",
"updatedAt": "2022-01-07T02:46:28.9270000Z",
"serviceBusEndpoint": "https://yicma-hub-namespace.servicebus.windows.net:443/",
"enabled": true,
"critical": false,
"zoneRedundant": false
},
"id": "/subscriptions//resourceGroups//providers/Microsoft.NotificationHubs/namespaces/",
"name": "",
"type": "Microsoft.NotificationHubs/namespaces",
"location": "East US",
"tags": {
"env": "Test"
}
}
```

Start with the notificationhubs.json definition at the referenced 2017-04-01 namespace schema and compare it with the supplied PUT and GET payloads. Reproduce the REST API behavior if possible, then determine whether the API specification or the service response is inconsistent; document the confirmed discrepancy and its expected resolution.

Written by the indexing model from the issue text.