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 
if subscriber.get('RawMessageDelivery') not in ('true', True):
        return {}
    message_attributes = {}
    for key, value in attributes.items():
        attribute = {}
        attribute['DataType'] = value['Type']
        if value['Type'] == 'Binary':
            attribute['BinaryValue'] = value['Value']
        else:
            attribute['StringValue'] = value['Value']
        message_attributes[key] = attribute
    return message_attributes
def get_message_attributes(req_data):