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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"""
    arn = func_arn(function)
    
    LAMBDA_EXECUTOR.cleanup(arn)
    try:
        arn_to_lambda.pop(arn)
    except KeyError:
        return not_found_error(func_arn(function))
    event_publisher.fire_event(event_publisher.EVENT_LAMBDA_DELETE_FUNC,
        payload={'n': event_publisher.get_hash(function)})
    i = 0
    while i < len(event_source_mappings):
        mapping = event_source_mappings[i]
        if mapping['FunctionArn'] == arn:
            del event_source_mappings[i]
            i -= 1
        i += 1
    result = {}
    return jsonify(result)
@app.route('%s/functions/<function>/code' % PATH_ROOT, methods=['PUT'])
def update_function_code(function):
    """ Update the code of an existing function
        ---
        operationId: 'updateFunctionCode'
        parameters:
            - name: 'request'
              in: body
    """
    data = json.loads(to_str(request.data))
    result = set_function_code(data, function)