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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'tags': 'Tags'
            }
        }
    }
}
def convert_acl_cf_to_s3(acl):
    """ Convert a CloudFormation ACL string (e.g., 'PublicRead') to an S3 ACL string (e.g., 'public-read') """
    return re.sub('(?<!^)(?=[A-Z])', '-', acl).lower()
def retrieve_topic_arn(topic_name):
    topics = aws_stack.connect_to_service('sns').list_topics()['Topics']
    topic_arns = [t['TopicArn'] for t in topics if t['TopicArn'].endswith(':%s' % topic_name)]
    return topic_arns[0]
def get_role_arn(role_arn, **kwargs):
    role_arn = resolve_refs_recursively(kwargs.get('stack_name'), role_arn, kwargs.get('resources'))
    return aws_stack.role_arn(role_arn)
def parse_template(template):
    try:
        return json.loads(template)
    except Exception:
        return yaml.safe_load(template)
def template_to_json(template):
    template = parse_template(template)
    return json.dumps(template)
def get_resource_type(resource):
    res_type = resource.get('ResourceType') or resource.get('Type') or ''
    parts = res_type.split('::', 1)
    if len(parts) == 1:
        return None
    return parts[1]
def get_service_name(resource):