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 
attributes = {}
    x = 1
    while True:
        name = req_data.get('MessageAttributes.entry.' + str(x) + '.Name', [None])[0]
        if name is not None:
            attribute = {}
            attribute['Type'] = req_data.get('MessageAttributes.entry.' + str(x) + '.Value.DataType', [None])[0]
            string_value = req_data.get('MessageAttributes.entry.' + str(x) + '.Value.StringValue', [None])[0]
            binary_value = req_data.get('MessageAttributes.entry.' + str(x) + '.Value.BinaryValue', [None])[0]
            if string_value is not None:
                attribute['Value'] = string_value
            elif binary_value is not None:
                attribute['Value'] = binary_value
            attributes[name] = attribute
            x += 1
        else:
            break
    return attributes
def is_number(x):