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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account_id = get_account_id(account_id)
    return ('arn:aws:firehose:%s:%s:deliverystream/%s' % (get_region(), account_id, stream_name))
def s3_bucket_arn(bucket_name, account_id=None):
    return 'arn:aws:s3:::%s' % (bucket_name)
def _resource_arn(name, pattern, account_id=None, region_name=None):
    if ':' in name:
        return name
    account_id = get_account_id(account_id)
    region_name = region_name or get_region()
    return pattern % (region_name, account_id, name)
def create_sqs_queue(queue_name, env=None):
    env = get_environment(env)
    
    conn = connect_to_service('sqs', env=env)
    return conn.create_queue(QueueName=queue_name)
def sqs_queue_arn(queue_name, account_id=None, region_name=None):
    account_id = get_account_id(account_id)
    region_name = region_name or get_region()
    return ('arn:aws:sqs:%s:%s:%s' % (region_name, account_id, queue_name))
def apigateway_restapi_arn(api_id, account_id=None, region_name=None):
    account_id = get_account_id(account_id)
    region_name = region_name or get_region()
    return ('arn:aws:apigateway:%s:%s:/restapis/%s' % (region_name, account_id, api_id))
def sqs_queue_name(queue_arn):
    parts = queue_arn.split(':')
    return queue_arn if len(parts) == 1 else parts[5]
def sns_topic_arn(topic_name, account_id=None):
    account_id = get_account_id(account_id)
    return ('arn:aws:sns:%s:%s:%s' % (get_region(), account_id, topic_name))
def get_sqs_queue_url(queue_arn):