=== AmqpForwardAttribute

This mailet forwards the attributes values to a AMPQ.

It takes 4 parameters:

* attribute (mandatory): content to be forwarded, expected to be a Map<String, byte[]>
where the byte[] content is issued from a MimeBodyPart.
It is typically generated from the StripAttachment mailet.
* uri (mandatory): AMQP URI defining the server where to send the attachment. High availability is supported with a
  coma separated list of uris, whost and credentials are taken from the first URI specified.
* exchange (mandatory): name of the AMQP exchange.
* exchange_type (optional, default to "direct"): type of the exchange. Can be "direct", "fanout", "topic", "headers".
* routing_key (optional, default to empty string): name of the routing key on this exchange.

This mailet will sent the data attached to the mail as an attribute holding a map.