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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cert.sign(k, 'sha1')
    cert_file = StringIO()
    key_file = StringIO()
    cert_file.write(to_str(crypto.dump_certificate(crypto.FILETYPE_PEM, cert)))
    key_file.write(to_str(crypto.dump_privatekey(crypto.FILETYPE_PEM, k)))
    cert_file_content = cert_file.getvalue().strip()
    key_file_content = key_file.getvalue().strip()
    file_content = '%s\n%s' % (key_file_content, cert_file_content)
    if target_file:
        key_file_name = '%s.key' % target_file
        cert_file_name = '%s.crt' % target_file
        
        
        if not os.path.exists(target_file):
            save_file(target_file, file_content)
            save_file(key_file_name, key_file_content)
            save_file(cert_file_name, cert_file_content)
            TMP_FILES.append(target_file)
            TMP_FILES.append(key_file_name)
            TMP_FILES.append(cert_file_name)
        if not return_content:
            return target_file, cert_file_name, key_file_name
    return file_content
def run_safe(_python_lambda, print_error=False, **kwargs):
    try:
        return _python_lambda(**kwargs)
    except Exception as e:
        if print_error:
            LOG.warning('Unable to execute function: %s' % e)
def run_cmd_safe(**kwargs):