* After introduction an `rsocketFrameType` header in the message,
we don't need a custom `IntegrationRSocket` any more.
Fully rely on the `MessagingRSocket` from the Spring Messaging, only
handle properly a `RSocketFrameTypeMessageCondition.CONNECT_CONDITION`
for connections from clients to emit an `RSocketConnectedEvent`
* Copy a `ChannelSendOperator` from the Spring Messaging for the proper
reply handling, when we are interested in the source `Publisher`
subscription first.
See its JavaDocs for more info
* Reusing already `public PayloadUtils` instead of its method copies
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