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.

<!-- Love localstack? Please consider supporting our collective:
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resource_type = get_resource_type(resource)
    entry = RESOURCE_TO_FUNCTION.get(resource_type)
    if entry is None:
        LOG.warning('Unknown resource type "%s": %s' % (resource_type, resource))
    return bool(entry and entry.get(ACTION_CREATE))
def is_deployed(resource_id, resources, stack_name):
    resource = resources[resource_id]
    resource_status = resource.get('__details__') or {}
    details = retrieve_resource_details(resource_id, resource_status, resources, stack_name)
    return bool(details)
def should_be_deployed(resource_id, resources, stack_name):
    """ Return whether the given resource is all of: (1) deployable, (2) not yet deployed,
        and (3) has no unresolved dependencies. """
    resource = resources[resource_id]
    if not is_deployable_resource(resource) or is_deployed(resource_id, resources, stack_name):
        return False
    res_deps = get_resource_dependencies(resource_id, resource, resources)
    return all_dependencies_satisfied(res_deps, stack_name, resources, resource_id)
def is_updateable(resource_id, resources, stack_name):
    """ Return whether the given resource can be updated or not """
    resource = resources[resource_id]
    if not is_deployable_resource(resource) or not is_deployed(resource_id, resources, stack_name):
        return False
    resource_type = get_resource_type(resource)
    return resource_type in UPDATEABLE_RESOURCES
def all_dependencies_satisfied(resources, stack_name, all_resources, depending_resource=None):