JIRA: https://jira.spring.io/browse/INT-4244
The `JpaOutboundGateway` returns a whole `Message` for reply copying request headers.
Building the reply a `AbstractMessageProducingHandler` uses `MessageBuilder` to create a new `Message` with all request headers because of `shouldCopyRequestHeaders() == true`
* To avoid some overhead with new `Message` and `MessageBuilder` for nothing, just return a JPA result as is and let super class to build the Message
* Optimize all reply producers to return `MessageBuilder` to the super `handleMessage()` process
* Return the whole `gatherResult` `Message<?>` from the `ScatterGatherHandler` to have ability to transfer reply headers as well
* Mark `DelayHandler` as `shouldCopyRequestHeaders() return false` since it doesn't modify Message and returns it as is after delay
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