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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props = cloudformation_json['Properties']
        name = props['StageName']
        deployment_id = props.get('Id') or short_uid()
        description = props.get('Description') or ''
        return apigw_models.Deployment(deployment_id, name, description)
    @classmethod
    def Resource_create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):
        props = cloudformation_json['Properties']
        region_name = props.get('Region') or aws_stack.get_region()
        path_part = props.get('PathPart')
        api_id = props.get('RestApiId')
        parent_id = props.get('ParentId')
        id = props.get('Id') or short_uid()
        return apigw_models.Resource(id, region_name, api_id, path_part, parent_id)
    @classmethod
    def Method_create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):
        props = cloudformation_json['Properties']
        method_type = props.get('HttpMethod')
        authorization_type = props.get('AuthorizationType')
        return apigw_models.Method(method_type, authorization_type)
    apigw_models.RestAPI.create_from_cloudformation_json = RestAPI_create_from_cloudformation_json
    apigw_models.RestAPI.get_cfn_attribute = RestAPI_get_cfn_attribute
    apigw_models.Deployment.create_from_cloudformation_json = Deployment_create_from_cloudformation_json
    apigw_models.Resource.create_from_cloudformation_json = Resource_create_from_cloudformation_json
    apigw_models.Method.create_from_cloudformation_json = Method_create_from_cloudformation_json
    
    
    def describe_stack_resource(self):