GH-3089: Add AmqpInGateway.replyHeadersMappedLast (#3091)

* GH-3089: Add AmqpInGateway.replyHeadersMappedLast

Fixes https://github.com/spring-projects/spring-integration/issues/3089

In some use-case we would like to control when headers from SI message
should be populated into an AMQP message.
One of the use-case is like a `SimpleMessageConverter` and its `plain/text`
for the String reply, meanwhile we know that this content is an
`application/json`.
So, with a new `replyHeadersMappedLast` we can override the mentioned
`content-type` header, populated by the `MessageConverter` with an
actual value from the message headers populated in the flow upstream

* Introduce an `AmqpInboundGateway.replyHeadersMappedLast`; expose it
on the DSL and XML level
* Use newly introduced `MappingUtils.mapReplyMessage()`
* Optimize `DefaultAmqpHeaderMapper` to not parse JSON headers at all
when `JsonHeaders.TYPE_ID` is already present (e.g. `MessageConverter`
result)
* Also skip `JsonHeaders` when we `populateUserDefinedHeader()`

**Cherry-pick to 5.1.x**

* * Fix language and package typos
* Add missed `@param` in JavaDoc of the `AmqpBaseInboundGatewaySpec.batchingStrategy()`
* Extract a `RabbitTemplate` `MessageConverter` to use for reply messages
conversion - pursue a backward compatibility

src/reference/asciidoc/amqp.adoc

@@ -1196,6 +1196,9 @@ The `ObjectToJsonTransformer` does exactly that (by default).
 
 There is now a property called `headersMappedLast` on the outbound channel adapter and gateway (as well as on AMQP-backed channels).
 Setting this to `true` restores the behavior of overwriting the property added by the converter.
+
+Starting with version 5.1.9, a similar `replyHeadersMappedLast` is provided for the `AmqpInboundGateway` when we produce a reply and would like to override headers populated by the converter.
+See its JavaDocs for more information.
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 [[amqp-user-id]]