Fix docs for version 4.0

* Move existing `What's New` to the respective `changes-in-3-2-since-3-1.adoc`
* Add entries for the current version into `What's New`
* Start new `rabbitmq-amqp-client.adoc` chapter

Author: artembilan

src/reference/antora/modules/ROOT/nav.adoc

@@ -57,6 +57,7 @@
 *** xref:amqp/multi-rabbit.adoc[]
 *** xref:amqp/debugging.adoc[]
 ** xref:stream.adoc[]
+** xref:rabbitmq-amqp-client.adoc[]
 ** xref:logging.adoc[]
 ** xref:sample-apps.adoc[]
 ** xref:testing.adoc[]

src/reference/antora/modules/ROOT/pages/appendix/previous-whats-new/changes-in-3-2-since-3-1.adoc

@@ -0,0 +1,17 @@
+[[changes-in-3-2-since-3-1]]
+= Changes in 3.2 Since 3.1
+
+[[spring-framework-6-2]]
+== Spring Framework 6.1
+
+This version requires Spring Framework 6.2.
+
+[[x32-consistent-hash-exchange]]
+== Consistent Hash Exchange
+
+The convenient `ConsistentHashExchange` and respective `ExchangeBuilder.consistentHashExchange()` API has been introduced.
+
+[[x32-retry-count-header]]
+== The `retry_count` header
+
+The `retry_count` header should be used now instead of relying on server side increment for the `x-death.count` property.

src/reference/antora/modules/ROOT/pages/rabbitmq-amqp-client.adoc

@@ -0,0 +1,8 @@
+[[amqp-client]]
+= RabbitMQ AMQP 1.0 Support
+
+Version 4.0 introduces `spring-rabbitmq-client` module for https://www.rabbitmq.com/client-libraries/amqp-client-libraries[AMQP 1.0] protocol support on RabbitMQ.
+
+This artifact is based on the {rabbitmq-github}/rabbitmq-amqp-java-client[com.rabbitmq.client:amqp-client] library and therefore can work only with RabbitMQ and its AMQP 1.0 protocol support.
+It cannot be used for any arbitrary AMQP 1.0 broker.
+For that purpose a https://qpid.apache.org/components/jms/index.html[JMS bridge] and respective {spring-framework-docs}/integration/jms.html[Spring JMS] integration is recommended so far.

src/reference/antora/modules/ROOT/pages/whats-new.adoc

@@ -2,20 +2,24 @@
 = What's New
 :page-section-summary-toc: 1
 
-[[changes-in-3-2-since-3-1]]
-== Changes in 3.2 Since 3.1
+[[changes-in-4-2-since-3-2]]
+== Changes in 4.0 Since 3.2
 
-[[spring-framework-6-2]]
-=== Spring Framework 6.1
+[[spring-framework-7-0]]
+=== Spring Framework 7.0
 
-This version requires Spring Framework 6.2.
+This version requires Spring Framework 7.0.
 
-[[x32-consistent-hash-exchange]]
-=== Consistent Hash Exchange
+[[x40-null-away]]
+=== Null-safety
 
-The convenient `ConsistentHashExchange` and respective `ExchangeBuilder.consistentHashExchange()` API has been introduced.
+As many other Spring portfolio projects, Spring AMQP has been migrated to https://jspecify.dev/docs/start-here[JSpecify] annotations to declare the nullness of API.
+The https://github.com/uber/NullAway[NullAway] Gradle plugin is used to check the consistency of null-safety declarations.
 
-[[x32-retry-count-header]]
-=== The `retry_count` header
+[[x40-rabbitmq-amqp-client]]
+=== The `spring-rabbitmq-client` module
 
-The `retry_count` header should be used now instead of relying on server side increment for the `x-death.count` property.
+The new `spring-rabbitmq-client` module (with same artifact name) is introduced.
+This is an implementation of AMQP 1.0 protocol specific to RabbitMQ since `4.0` and based on the `com.rabbitmq.client:amqp-client` library.
+
+See xref:rabbitmq-amqp-client.adoc[] for more information.