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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cloudformation = aws_stack.connect_to_service('cloudformation')
    response = cloudformation.describe_stack_resources(StackName=stack_name)
    for resource in response['StackResources']:
        if resource['LogicalResourceId'] == resource_logical_id:
            return resource
def list_stack_resources(stack_name):
    cloudformation = aws_stack.connect_to_service('cloudformation')
    response = cloudformation.list_stack_resources(StackName=stack_name)
    return response['StackResourceSummaries']
def get_queue_urls():
    sqs = aws_stack.connect_to_service('sqs')
    response = sqs.list_queues()
    return response['QueueUrls']
def get_topic_arns():
    sqs = aws_stack.connect_to_service('sns')
    response = sqs.list_topics()
    return [t['TopicArn'] for t in response['Topics']]
class CloudFormationTest(unittest.TestCase):
    def test_apply_template(self):
        cloudformation = aws_stack.connect_to_resource('cloudformation')
        s3 = aws_stack.connect_to_service('s3')
        template = template_deployer.template_to_json(load_file(TEST_TEMPLATE_1))
        
        cloudformation.create_stack(StackName=TEST_STACK_NAME, TemplateBody=template)
        
        def check_stack():