Hi, I'm trying to get LocalStack set up for integration testing and having a lot of trouble building CloudFormation templates that include nested stacks referenced via the `TemplateURL` property. Is this just not a thing that works in LocalStack? I've tried setting TemplateURL to a local file as well as to an object in an S3 bucket created with LocalStack.

For example if I call `create-stack` on a `template.yaml` containing the following:
```
Resources:
  SNSTopics:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: http://localhost:4572/artifacts/sns.yaml
```

...the stack builds but the referenced `sns.yaml` stack does not get built; whereas if I call `create-stack` directly on the referenced file it builds fine.

Thanks for any help/advice you can give!
result = configure_resource_via_sdk(resource_id, resources, resource_type, func, stack_name)
            results.append(result)
    return (results or [None])[0]
def configure_resource_via_sdk(resource_id, resources, resource_type, func_details, stack_name):
    resource = resources[resource_id]
    client = get_client(resource, func_details)
    function = getattr(client, func_details['function'])
    params = func_details.get('parameters') or lambda_get_params()
    defaults = func_details.get('defaults', {})
    if 'Properties' not in resource:
        resource['Properties'] = {}
    resource_props = resource['Properties']
    if callable(params):
        params = params(resource_props, stack_name=stack_name, resources=resources)
    else:
        params = dict(params)
        for param_key, prop_keys in dict(params).items():
            params.pop(param_key, None)
            if not isinstance(prop_keys, list):
                prop_keys = [prop_keys]
            for prop_key in prop_keys:
                if prop_key == PLACEHOLDER_RESOURCE_NAME:
                    params[param_key] = resource_id
                    resource_name = get_resource_name(resource)
                    if resource_name:
                        params[param_key] = resource_name
                    else:
                        
                        try:
                            return resolve_ref(stack_name, resource_id, resources,