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 = get_stack_details(TEST_STACK_NAME)
            self.assertEqual(stack['StackStatus'], 'CREATE_COMPLETE')
        retry(check_stack, retries=3, sleep=2)
        
        assert bucket_exists('cf-test-bucket-1')
        
        assert queue_exists('cf-test-queue-1')
        
        assert topic_exists('cf-test-topic-1-1')
        
        assert stream_exists('cf-test-stream-1')
        
        resource = describe_stack_resource(TEST_STACK_NAME, 'SQSQueueNoNameProperty')
        assert queue_exists(resource['PhysicalResourceId'])
        
        tags = s3.get_bucket_tagging(Bucket='cf-test-bucket-1')['TagSet']
        self.assertEqual(tags, [{'Key': 'foobar', 'Value': aws_stack.get_sqs_queue_url('cf-test-queue-1')}])
    def test_list_stack_events(self):
        cloudformation = aws_stack.connect_to_service('cloudformation')
        response = cloudformation.describe_stack_events()
        self.assertEqual(response['ResponseMetadata']['HTTPStatusCode'], 200)
    def test_validate_template(self):
        cloudformation = aws_stack.connect_to_service('cloudformation')
        template = template_deployer.template_to_json(load_file(TEST_TEMPLATE_1))
        response = cloudformation.validate_template(TemplateBody=template)
        self.assertEqual(response['ResponseMetadata']['HTTPStatusCode'], 200)
    def test_validate_invalid_json_template_should_fail(self):