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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resource = resources[resource_id]
    client = get_client(resource)
    if not client:
        return False
    resource_type = get_resource_type(resource)
    func_details = RESOURCE_TO_FUNCTION.get(resource_type)
    if not func_details:
        LOG.warning('Resource type not yet implemented: %s' % resource_type)
        return
    LOG.debug('Deploying resource type "%s" id "%s"' % (resource_type, resource_id))
    func_details = func_details[ACTION_CREATE]
    function = getattr(client, func_details['function'])
    params = func_details['parameters']
    defaults = func_details.get('defaults', {})
    if 'Properties' not in resource:
        resource['Properties'] = {}
    resource_props = resource['Properties']
    if callable(params):
        params = params(resource_props, stack_name=stack_name, resources=resources)
    else:
        params = dict(params)
        for param_key, prop_keys in dict(params).items():
            params.pop(param_key, None)