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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if lambda_cwd:
            previous_cwd = os.getcwd()
            os.chdir(lambda_cwd)
            sys.path = [lambda_cwd] + sys.path
        if lambda_env:
            previous_env = dict(os.environ)
            os.environ.update(lambda_env)
    
    lambda_id = 'l_%s' % short_uid()
    lambda_file = LAMBDA_SCRIPT_PATTERN.replace('*', lambda_id)
    save_file(lambda_file, script)
    
    TMP_FILES.append(lambda_file)
    TMP_FILES.append('%sc' % lambda_file)
    try:
        handler_module = imp.load_source(lambda_id, lambda_file)
        module_vars = handler_module.__dict__
    except Exception as e:
        LOG.error('Unable to exec: %s %s' % (script, traceback.format_exc()))
        raise e
    finally:
        if lambda_cwd or lambda_env:
            if lambda_cwd:
                os.chdir(previous_cwd)
                sys.path.pop(0)
            if lambda_env:
                os.environ = previous_env
            exec_mutex.release()
    return module_vars[handler_function]
def get_handler_file_from_name(handler_name, runtime=LAMBDA_DEFAULT_RUNTIME):