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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if files:
        cleanup_tmp_files()
def cleanup_threads_and_processes(quiet=True):
    for t in TMP_THREADS:
        t.stop(quiet=quiet)
    for p in TMP_PROCESSES:
        try:
            p.terminate()
        except Exception as e:
            print(e)
    
    clear_list(TMP_THREADS)
    clear_list(TMP_PROCESSES)
def clear_list(l):
    while len(l):
        del l[0]
def cleanup_tmp_files():
    for tmp in TMP_FILES:
        try:
            rm_rf(tmp)
        except Exception:
            pass  
    del TMP_FILES[:]
def new_tmp_file():
    """ Return a path to a new temporary file. """
    tmp_file, tmp_path = tempfile.mkstemp()
    os.close(tmp_file)
    TMP_FILES.append(tmp_path)
    return tmp_path
def new_tmp_dir():