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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original_resource, new_resource_name, cloudformation_json, region_name):
        resource_name = cloudformation_json.get('Properties', {}).get('FunctionName') or new_resource_name
        return Lambda_create_from_cloudformation_json_orig(resource_name, cloudformation_json, region_name)
    if not hasattr(lambda_models.LambdaFunction, 'update_from_cloudformation_json'):
        lambda_models.LambdaFunction.update_from_cloudformation_json = Lambda_update_from_cloudformation_json
    
    def depl_delete_from_cloudformation_json(
            resource_name, resource_json, region_name):
        properties = resource_json['Properties']
        LOG.info('TODO: apigateway.Deployment.delete_from_cloudformation_json %s' % properties)
    if not hasattr(apigw_models.Deployment, 'delete_from_cloudformation_json'):
        apigw_models.Deployment.delete_from_cloudformation_json = depl_delete_from_cloudformation_json
    
    def vers_delete_from_cloudformation_json(
            resource_name, resource_json, region_name):
        properties = resource_json['Properties']
        LOG.info('TODO: apigateway.Deployment.delete_from_cloudformation_json %s' % properties)
    if not hasattr(lambda_models.LambdaVersion, 'delete_from_cloudformation_json'):
        lambda_models.LambdaVersion.delete_from_cloudformation_json = vers_delete_from_cloudformation_json
    
    parsing.MODEL_MAP['AWS::ApiGateway::Deployment'] = apigw_models.Deployment
    parsing.MODEL_MAP['AWS::ApiGateway::Method'] = apigw_models.Method
    parsing.MODEL_MAP['AWS::ApiGateway::Resource'] = apigw_models.Resource
    parsing.MODEL_MAP['AWS::ApiGateway::RestApi'] = apigw_models.RestAPI
    parsing.MODEL_MAP['AWS::StepFunctions::StateMachine'] = sfn_models.StateMachine
    @classmethod
    def RestAPI_create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):