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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stack_name = resources_map.get('AWS::StackName')
        resource_hash_key = (stack_name, logical_id)
        
        updating = CURRENTLY_UPDATING_RESOURCES.get(resource_hash_key)
        LOG.debug('Currently updating stack resource %s/%s: %s' % (stack_name, logical_id, updating))
        if updating:
            return None
        
        resource_tuple = parsing.parse_resource(logical_id, resource_json, resources_map)
        if not resource_tuple:
            return None
        _, resource_json, _ = resource_tuple
        
        props = resource_json['Properties'] = resource_json.get('Properties') or {}
        if resource_json['Type'] == 'AWS::Lambda::EventSourceMapping' and not props.get('StartingPosition'):
            props['StartingPosition'] = 'LATEST'
        
        resource = resources_map._parsed_resources.get(logical_id)
        if resource and not update:
            return resource
        
        resource_wrapped = {logical_id: resource_json}
        should_be_created = template_deployer.should_be_deployed(logical_id, resource_wrapped, stack_name)
        if not should_be_created:
            
            if not template_deployer.is_updateable(logical_id, resource_wrapped, stack_name):