RabbitMQConsumer: Publish the message routing key as an attribute to flowfile

When retrieving messages from a queue that is bound to a topic exchange, message come with a routing key which might contain crucial identifying information about where the message came from.

Current implementation of the RabbitMQConsumer processor doesn't publish this property of the message to the attributes of the flowfile it creates. Can this be added?

I found the relevant code here: https://github.com/apache/nifi/blob/d838f61291d2582592754a37314911b701c6891b/nifi-nar-bundles/nifi-amqp-bundle/nifi-amqp-processors/src/main/java/org/apache/nifi/amqp/processors/AMQPUtils.java#L95

I have very sketchy Java skills, otherwise would submit a PR.