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!
res_type = resource.get('Type', resource.get('ResourceType', ''))
    parts = res_type.split('::')
    if len(parts) == 1:
        return None
    if res_type.endswith('Cognito::UserPool'):
        return 'cognito-idp'
    if parts[-2] == 'Cognito':
        return 'cognito-idp'
    return parts[1].lower()
def get_resource_name(resource):
    res_type = get_resource_type(resource)
    properties = resource.get('Properties') or {}
    name = properties.get('Name')
    if name:
        return name
    
    if res_type == 'S3::Bucket':
        name = properties.get('BucketName')
    elif res_type == 'SQS::Queue':
        name = properties.get('QueueName')
    elif res_type == 'Cognito::UserPool':
        name = properties.get('PoolName')
    elif res_type == 'StepFunctions::StateMachine':
        name = properties.get('StateMachineName')
    else:
        LOG.warning('Unable to extract name for resource type "%s"' % res_type)
    return name
def get_client(resource, func_config):