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 sys
import logging
import traceback
import six
from moto.s3 import models as s3_models
from moto.iam import models as iam_models
from moto.sqs import models as sqs_models
from moto.core import BaseModel
from moto.server import main as moto_main
from moto.dynamodb import models as dynamodb_models
from moto.dynamodb2 import models as dynamodb2_models
from moto.awslambda import models as lambda_models
from moto.apigateway import models as apigw_models
from moto.cloudformation import parsing, responses
from boto.cloudformation.stack import Output
from moto.cloudformation.exceptions import ValidationError, UnformattedGetAttTemplateException
from localstack import config
from localstack.constants import DEFAULT_PORT_CLOUDFORMATION_BACKEND, TEST_AWS_ACCOUNT_ID, MOTO_ACCOUNT_ID
from localstack.utils.aws import aws_stack
from localstack.utils.common import FuncThread, short_uid, recurse_object, clone, json_safe
from localstack.stepfunctions import models as sfn_models
from localstack.services.infra import (
    get_service_protocol, start_proxy_for_service, do_run, canonicalize_api_names)
from localstack.utils.bootstrap import setup_logging
from localstack.utils.cloudformation import template_deployer
from localstack.services.cloudformation import service_models