Restore documentation on `reject-publish-dlx`
Restore documentation on `reject-publish-dlx`

See rabbitmq/rabbitmq-server#1443, rabbitmq/rabbitmq-server#2015

rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website,rabbitmq/rabbitmq-website