Hi

I have issues creating sns subscriptions through Cloudformation. If I attempt to include a `AWS::SNS::Subscription` resource in a Cloudformation template and run `create-stack` then I get a 500 Internal Server error. The full template:

```
AWSTemplateFormatVersion: '2010-09-09'
Description: 'Test'
Resources:
  MySnsTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: MySnsTopic
  MySnsTopicSubscription:
    Type: AWS::SNS::Subscription
    Properties:
      Protocol: sqs
      TopicArn: !Ref MySnsTopic
      Endpoint: !GetAtt
        - MySqsQueue
        - QueueArn
  MySqsQueue:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: MySqsQueue
```

If I replace the references with hard-coded arns like this:

```
TopicArn: arn:aws:sns:eu-west-2:123456789012:MySnsTopic
Endpoint: arn:aws:sqs:elasticmq:000000000000:MySqsQueue
```

Then I get no errors but I get a warning:

`No moto Cloudformation support for AWS::SNS::Subscription`.

I can get around this issue by creating the subscription when creating the topic but the issue there is that I cannot add any attributes and in my case I need `RawMessageDelivery` set to true. So my questions are:

1. Is there no support to create `AWS::SNS::Subscription` resources through Cloudformation or am I doing something wrong?
2. If support is not there can I request it as a new feature?
3. Any suggestions on how I can work around this? I know I could do this through a script at startup but would like to not have any additional script steps other than deploying the Cloudformation stack.

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params = common.merge_recursive(defaults, params)
    
    params = convert_data_types(func_details, params)
    
    try:
        LOG.debug('Request for creating resource type "%s": %s %s' % (
            resource_type, func_details['function'], params))
        result = function(**params)
    except Exception as e:
        LOG.warning('Error calling %s with params: %s for resource: %s' % (function, params, resource))
        raise e
    
    if resource_type == 'ApiGateway::Method':
        integration = resource_props.get('Integration')
        if integration:
            api_id = resolve_refs_recursively(stack_name, resource_props['RestApiId'], resources)
            res_id = resolve_refs_recursively(stack_name, resource_props['ResourceId'], resources)
            uri = integration.get('Uri')
            if uri:
                uri = resolve_refs_recursively(stack_name, uri, resources)
                aws_stack.connect_to_service('apigateway').put_integration(restApiId=api_id, resourceId=res_id,
                    httpMethod=resource_props['HttpMethod'], type=integration['Type'],
                    integrationHttpMethod=integration['IntegrationHttpMethod'], uri=uri
                )
    elif resource_type == 'SNS::Topic':
        subscriptions = resource_props.get('Subscription', [])
        for subscription in subscriptions:
            endpoint = resolve_refs_recursively(stack_name, subscription['Endpoint'], resources)
            topic_arn = retrieve_topic_arn(params['Name'])