GH-9695: Replace AMQP tx-size with batch-size

Fixes: #9695
Issue link: https://github.com/spring-projects/spring-integration/issues/9695

The `txSize` in the `SimpleMessageListenerContainer` has been replaced with more reasonable `batchSize`.
Spring Integration XML support for AMQP module has missed to fix this change: we didn't have a respective test.

* Deprecate `tx-size` (will be removed in `6.5`) XML attribute for the `<amqp:inbound-channel-adapter>`
and introduce `batch-size`
* Cover with the tests
* Fix docs from `tx-size` to `batch-size`

**Auto-cherry-pick to `6.3.x`**

src/reference/antora/modules/ROOT/pages/amqp.adoc

@@ -32,7 +32,7 @@ The following adapters are available:
 * xref:amqp/inbound-gateway.adoc[Inbound Gateway]
 * xref:amqp/outbound-channel-adapter.adoc[Outbound Channel Adapter]
 * xref:amqp/outbound-gateway.adoc[Outbound Gateway]
-* xref:amqp-async-outbound-gateway[Async Outbound Gateway]
+* xref:amqp/async-outbound-gateway.adoc[Async Outbound Gateway]
 * xref:amqp/rmq-streams.adoc#rmq-stream-inbound-channel-adapter[RabbitMQ Stream Queue Inbound Channel Adapter]
 * xref:amqp/rmq-streams.adoc#rmq-stream-outbound-channel-adapter[RabbitMQ Stream Queue Outbound Channel Adapter]
 

src/reference/antora/modules/ROOT/pages/amqp/inbound-channel-adapter.adoc

@@ -87,7 +87,7 @@ XML::
                                   task-executor=""                <22>
                                   transaction-attribute=""        <23>
                                   transaction-manager=""          <24>
-                                  tx-size=""                      <25>
+                                  batch-size=""                   <25>
                                   consumers-per-queue             <26>
                                   batch-mode="MESSAGES"/>         <27>
 
@@ -146,7 +146,7 @@ By default, this value is `Integer.MAX_VALUE`, meaning that this container start
 Optional.
 <17> Tells the AMQP broker how many messages to send to each consumer in a single request.
 Often, you can set this value high to improve throughput.
-It should be greater than or equal to the transaction size (see the `tx-size` attribute, later in this list).
+It should be greater than or equal to the transaction size (see the `batch-size` attribute, later in this list).
 Optional (defaults to `1`).
 <18> Receive timeout in milliseconds.
 Optional (defaults to `1000`).
@@ -173,7 +173,7 @@ If the `channelTransacted` flag is `false`, no transaction semantics apply to th
 For further information, see
 https://docs.spring.io/spring-amqp/reference/html/%255Freference.html#%5Ftransactions[Transactions with Spring AMQP].
 Optional.
-<25> Tells the `SimpleMessageListenerContainer` how many messages to process in a single transaction (if the channel is transactional).
+<25> Tells the `SimpleMessageListenerContainer` how many messages to process in a single request.
 For best results, it should be less than or equal to the value set in `prefetch-count`.
 Not allowed when 'consumers-per-queue' is set.
 Optional (defaults to `1`).

src/reference/antora/modules/ROOT/pages/amqp/inbound-gateway.adoc

@@ -10,7 +10,7 @@ Java DSL::
 +
 [source, java, role="primary"]
 ----
-@Bean // return the upper cased payload
+@Bean // return the upper-cased payload
 public IntegrationFlow amqpInboundGateway(ConnectionFactory connectionFactory) {
     return IntegrationFlow.from(Amqp.inboundGateway(connectionFactory, "foo"))
             .transform(String.class, String::toUpperCase)