Hello,
I am working with a SNS to SQS project, in it we want to use the feature `RawMessageBody` when subscribing.
By looking into the code I found that the attributes are not persisted, for example `RawMessageBody` is always set to 'false'. Elsewhere in the code the parameters seems to be correctly used and send transform the message accordingly.

I created a PR fixing this : https://github.com/localstack/localstack/pull/1234
Thank you 
message = req_data['Message'][0]
    subject = req_data.get('Subject', [None])[0]
    protocol = subscriber['Protocol']
    if six.PY2 and type(message).__name__ == 'unicode':
        
        message = message.encode('raw-unicode-escape')
    if subscriber.get('RawMessageDelivery') in ('true', True):
        return message
    if req_data.get('MessageStructure') == ['json']:
        message = json.loads(message)
        try:
            message = message.get(protocol, message['default'])
        except KeyError:
            raise Exception("Unable to find 'default' key in message payload")
    data = {}
    data['MessageId'] = str(uuid.uuid4())
    data['Type'] = 'Notification'
    data['Message'] = message
    data['TopicArn'] = subscriber['TopicArn']
    if subject is not None:
        data['Subject'] = subject
    attributes = get_message_attributes(req_data)
    if attributes:
        data['MessageAttributes'] = attributes
    result = json.dumps(data)
    return result
def create_sqs_message_attributes(subscriber, attributes):