Since the DSL code is new in this version there is no reason to keep deprecated method
* Remove deprecated `resequence()` and `aggregate()` in the `IntegrationFlowDefinition`
* Remove `InternalAggregatingMessageHandler` with the `MessageGroupProcessorWrapper` delegation logic in favor of newly introduced `AbstractCorrelatingMessageHandler.setOutputProcessor()`
* Rework `Promise` Gateway Docs to the `Mono`
* Rename `AsyncGatewayTests` "promise" words to "mono"
* Resolve `com.rabbitmq.client.FlowListener` deprecation
RecipientListRouter DSL refactoring
Previously there was a DSL specific `DslRecipientListRouter` to overcome the lack of setters in the target `RecipientListRouter` and its `Recipient`
* Add `channelName` variant for the `Recipient`
* Add several new `addRecipient()` methods to the `RecipientListRouter`
All those improvements allow to avoid extra bridge (or adapter) component between Java DSL and target `RecipientListRouter`
* Make `LambdaMessageProcessor` and `GatewayMessageHandler` as `public` classes and move them to the appropriate packages
Address PR comments
Add `isLambda()` condition to `RecipientListRouterSpec` to avoid ambiguity for the provided `GenericSelector` impl
checkstyle polishing
092d876fae