JIRA: https://jira.spring.io/browse/INT-4264
When we use Java DSL `.publishSubscribeChannel()`, we expect that subscribers
will be called in the order they are defined in the flow.
But actually everything is depend on the populated `MessageHandler` implementation.
The `AbstractMessageHandler` implements `Ordered` and according the
`OrderedAwareCopyOnWriteArraySet` logic they are placed in the beginning of the
handlers set, meanwhile all others (un-ordered) are moved to the end.
* Add implicit `.bridge()` to all the subFlows added to the `PublishSubscribeSpec`.
This way all the subFlow subscribers will be ordered the same way (because of
`BridgeHandler`) and, therefore, will be preformed in the expected (as declared) order
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