Upgrade to SI 4.0

* Add new correlation endpoint options
* Add `messageStore` to the `PriorityChannelSpec`
* Add generic to `EnricherSpec#property`
* Remove `type` from `EnricherSpec.headerExpression`
* Add `initialDelay` for `PeriodicTriggerSpec`
* Fix `IntegrationFlowBuilder` bugs, when there is no relevant the end of the flow
* Add embedded MongoDb support for tests
* Add `priority` test with `MongoDbChannelMessageStore`