* Fix a logic in the IntFlowDef.toReactivePublisher
* We may consider to start a `Publisher<Message<?>>` just from one
channel.
So, and an implicit `bridge()` to meet and internal `IntegrationFlow`
logic
* The `MessageChannelReference` and `FixedSubscriberChannelPrototype`
can't be converted to the reactive `Publisher`.
So, an implicit `bridge()` in between them and target `FluxMessageChannel`
NOTE: This maybe considered for back-port, but the workaround is
simple: just add extra `bridge()` after the mentioned channels
* * Allow `log()` before `toReactivePublisher()` and the same time fix
the problem with not resetted `implicitChannel` flag in the
`IntegrationFlowDefinition`
6c379d7199