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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'function': 'create_resource',
            'parameters': {
                'restApiId': 'RestApiId',
                'pathPart': 'PathPart',
                'parentId': 'ParentId'
            }
        }
    },
    'ApiGateway::Method': {
        'create': {
            'function': 'put_method',
            'parameters': {
                'restApiId': 'RestApiId',
                'resourceId': 'ResourceId',
                'httpMethod': 'HttpMethod',
                'authorizationType': 'AuthorizationType',
                'requestParameters': 'RequestParameters'
            }
        }
    },
    'ApiGateway::Method::Integration': {
    },
    'ApiGateway::Deployment': {
        'create': {
            'function': 'create_deployment',
            'parameters': {
                'restApiId': 'RestApiId',
                'stageName': 'StageName',
                'stageDescription': 'StageDescription',
                'description': 'Description'