[BUG] `ApiCenter.Management` @ `2024-03-01` - `PUT` operation for Services requires SKU

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/apicenter/ApiCenter.Management/Service.tsp

### API Spec version

2024-03-01

### Describe the bug

In the API Center API specification, there is no mention of `SKU` in the Create Or Update operation (PUT) for Services.
However, if you do not specify the `SKU` in the request body, you cannot update the Services in API Center.

When `SKU` is not present

When `SKU` is present


### Expected behavior

`PUT https://management.azure.com/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ApiCenter/services/{serviceName}?api-version=2024-03-01`

Request body

```json
{
"location": "East US",
"tags": {
"foo": "bar"
}
}
```

Response

```json
{
"type": "Microsoft.ApiCenter/services",
"location": "East US",
"sku": {
"name": "Free"
},
"properties": {},
"id": "/subscriptions/{{subscriptionId}}/resourceGroups/{{resourceGroupName}}/providers/Microsoft.ApiCenter/services/{{serviceName}}",
"name": "{{serviceName}}",
"tags": {
"foo": "bar"
},
"systemData": {
"createdAt": "2024-06-03T17:34:20.5622751Z",
"lastModifiedAt": "2024-06-19T13:29:55.4211607Z"
}
}
```

### Actual behavior

Response

```json
{
"code": "ValidationError",
"message": "The Sku property on the given model is null. A valid Sku is required to create or update an API Catalog."
}
```

### Reproduction Steps

1. Create API Center resource via Azure Portal
2. Update API Center resource via REST API

### Environment

_No response_