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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from OpenSSL import crypto
    if target_file and not overwrite and os.path.exists(target_file):
        key_file_name = '%s.key' % target_file
        cert_file_name = '%s.crt' % target_file
        return target_file, cert_file_name, key_file_name
    if random and target_file:
        if '.' in target_file:
            target_file = target_file.replace('.', '.%s.' % short_uid(), 1)
        else:
            target_file = '%s.%s' % (target_file, short_uid())
    
    k = crypto.PKey()
    k.generate_key(crypto.TYPE_RSA, 1024)
    
    cert = crypto.X509()
    subj = cert.get_subject()
    subj.C = 'AU'
    subj.ST = 'Some-State'
    subj.L = 'Some-Locality'
    subj.O = 'LocalStack Org'  
    subj.OU = 'Testing'
    subj.CN = 'LocalStack'
    serial_number = serial_number or 1001
    cert.set_serial_number(serial_number)
    cert.gmtime_adj_notBefore(0)
    cert.gmtime_adj_notAfter(10 * 365 * 24 * 60 * 60)
    cert.set_issuer(cert.get_subject())
    cert.set_pubkey(k)