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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import shutil
import requests
import dns.resolver
from io import BytesIO
from contextlib import closing
from datetime import datetime
from six import with_metaclass
from six.moves import cStringIO as StringIO
from six.moves.urllib.parse import urlparse
from multiprocessing.dummy import Pool
from localstack import config
from localstack.config import DEFAULT_ENCODING
from localstack.constants import ENV_DEV
from localstack.utils import bootstrap
from localstack.utils.bootstrap import FuncThread
TMP_FILES = []
TMP_THREADS = []
TMP_PROCESSES = []
CACHE_CLEAN_TIMEOUT = 60 * 5
CACHE_MAX_AGE = 60 * 60
CACHE_FILE_PATTERN = os.path.join(tempfile.gettempdir(), '_random_dir_', 'cache.*.json')
last_cache_clean_time = {'time': 0}
mutex_clean = threading.Semaphore(1)
TIMESTAMP_FORMAT = '%Y-%m-%dT%H:%M:%S'
TIMESTAMP_FORMAT_MILLIS = '%Y-%m-%dT%H:%M:%S.%fZ'
CODEC_HANDLER_UNDERSCORE = 'underscore'
DOWNLOAD_CHUNK_SIZE = 1024 * 1024
LOG = logging.getLogger(__name__)
INFRA_STOPPED = False
class CustomEncoder(json.JSONEncoder):