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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result = clean_json_orig(resource_json, resources_map)
        if isinstance(result, BaseModel):
            if isinstance(resource_json, dict) and 'Ref' in resource_json:
                entity_id = get_entity_id(result, resource_json)
                if entity_id:
                    return entity_id
                LOG.warning('Unable to resolve "Ref" attribute for: %s - %s - %s',
                            resource_json, result, type(result))
        return result
    clean_json_orig = parsing.clean_json
    parsing.clean_json = clean_json
    
    parsing.MODEL_MAP.update(MODEL_MAP)
    
    def parse_and_create_resource(logical_id, resource_json, resources_map, region_name):
        try:
            return _parse_and_create_resource(logical_id, resource_json, resources_map, region_name)
        except Exception as e:
            LOG.error('Unable to parse and create resource "%s": %s %s' %
                      (logical_id, e, traceback.format_exc()))
            raise
    def parse_and_update_resource(logical_id, resource_json, resources_map, region_name):
        try:
            return _parse_and_create_resource(logical_id,
                resource_json, resources_map, region_name, update=True)
        except Exception as e:
            LOG.error('Unable to parse and update resource "%s": %s %s' %
                      (logical_id, e, traceback.format_exc()))
            raise
    def _parse_and_create_resource(logical_id, resource_json, resources_map, region_name, update=False):