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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version = version or '$LATEST'
    result = {
        'CodeSha256': func_details.get_version(version).get('CodeSha256'),
        'Role': func_details.role,
        'Version': version,
        'FunctionArn': func_details.arn(),
        'FunctionName': func_details.name(),
        'CodeSize': func_details.get_version(version).get('CodeSize'),
        'Handler': func_details.handler,
        'Runtime': func_details.runtime,
        'Timeout': func_details.timeout,
        'Description': func_details.description,
        'MemorySize': func_details.memory_size,
        'LastModified': func_details.last_modified,
        'TracingConfig': {'Mode': 'PassThrough'},
        'RevisionId': func_details.get_version(version).get('RevisionId')
    }
    if func_details.envvars:
        result['Environment'] = {
            'Variables': func_details.envvars
        }
    if (always_add_version or version != '$LATEST') and len(result['FunctionArn'].split(':')) <= 7:
        result['FunctionArn'] += ':%s' % (version)
    return result
def forward_to_fallback_url(func_arn, data):