Add priority support for int-jms:channel

1. Spring integration introduced DynamicJmsTemplate for QOS support.
Although <int-jms:channel> is initialized using DynamicJmsTemplate, its implementation does not provide any option to set JMS message priority explicitly.

DynamicJmsTemplateProperties class is private, restricting any option to change this behavior.

Consider adding QOS option to <int-jms:channel> aggregate and priority handling on AbstractJmsChannel.doSend execution.

2. javax.jms.Message interface has its own JMSPriority, JMSDeliveryMode, JMSExpiration properties. Why not using them instead of complicated DynamicJmsTemplateProperties workaround? Consider adding JMS Template class option to <int-jms:channel> for manual JmsTemplate.doSend implementation.