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 localstack.services.awslambda import lambda_executors
from localstack.services.awslambda.lambda_executors import (
    LAMBDA_RUNTIME_PYTHON27,
    LAMBDA_RUNTIME_PYTHON36,
    LAMBDA_RUNTIME_NODEJS,
    LAMBDA_RUNTIME_NODEJS610,
    LAMBDA_RUNTIME_NODEJS810,
    LAMBDA_RUNTIME_JAVA8,
    LAMBDA_RUNTIME_DOTNETCORE2,
    LAMBDA_RUNTIME_DOTNETCORE21,
    LAMBDA_RUNTIME_GOLANG,
    LAMBDA_RUNTIME_RUBY,
    LAMBDA_RUNTIME_RUBY25,
    LAMBDA_RUNTIME_CUSTOM_RUNTIME)
from localstack.utils.common import (to_str, load_file, save_file, TMP_FILES, ensure_readable,
    mkdir, unzip, is_zip_file, run, short_uid, is_jar_archive, timestamp, TIMESTAMP_FORMAT_MILLIS,
    md5, new_tmp_file, parse_chunked_data, is_number, now_utc, safe_requests, isoformat_milliseconds)
from localstack.utils.aws import aws_stack, aws_responses
from localstack.utils.analytics import event_publisher
from localstack.utils.aws.aws_models import LambdaFunction
from localstack.utils.cloudwatch.cloudwatch_util import cloudwatched
APP_NAME = 'lambda_api'
PATH_ROOT = '/2015-03-31'
ARCHIVE_FILE_PATTERN = '%s/lambda.handler.*.jar' % config.TMP_FOLDER
LAMBDA_SCRIPT_PATTERN = '%s/lambda_script_*.py' % config.TMP_FOLDER
LAMBDA_RUNTIMES = [LAMBDA_RUNTIME_PYTHON27, LAMBDA_RUNTIME_PYTHON36,
    LAMBDA_RUNTIME_DOTNETCORE2, LAMBDA_RUNTIME_DOTNETCORE21, LAMBDA_RUNTIME_NODEJS,
    LAMBDA_RUNTIME_NODEJS610, LAMBDA_RUNTIME_NODEJS810, LAMBDA_RUNTIME_JAVA8, LAMBDA_RUNTIME_RUBY,
    LAMBDA_RUNTIME_RUBY25]
LAMBDA_DEFAULT_TIMEOUT = 3