JIRA: https://jira.spring.io/browse/INT-4131 Specify an expression on the outbound endpoints to set the `x-delay` header when using the RabbitMQ Delayed Message Exchange plugin. Polishing - PR Comments - Add `setDelay` - Port `FunctionExpression` from DSL - Add `SupplierExpression` Javadoc Fixes Use ValueExpression for delay * Simple polishing for `SupplierExpression` * Mention plain `delay` property in the `amqp.adoc`