Update Docs For Overriding Boot Dependencies (#2564)

Author: garyrussell

spring-kafka-docs/src/main/asciidoc/appendix.adoc

@@ -4,12 +4,16 @@
 When using Spring for Apache Kafka in a Spring Boot application, the Apache Kafka dependency versions are determined by Spring Boot's dependency management.
 If you wish to use a different version of `kafka-clients` or `kafka-streams`, and use the embedded kafka broker for testing, you need to override their version used by Spring Boot dependency management and add two `test` artifacts for Apache Kafka.
 
+Or, to use a different Spring for Apache Kafka version with a supported Spring Boot version, set the `spring-kafka.version` property.
+For example, {project-version} is supported by Spring Boot 2.7.x which brings in 2.8.x by default.
+
 ====
 [source, xml, subs="+attributes", role="primary"]
 .Maven
 ----
 <properties>
     <kafka.version>3.2.3</kafka.version>
+    <spring-kafka.version>{project-version}</spring-kafka.version>
 </properties>
 
 <dependency>
@@ -33,6 +37,7 @@ If you wish to use a different version of `kafka-clients` or `kafka-streams`, an
 .Gradle
 ----
 ext['kafka.version'] = '3.2.3'
+ext['spring-kafka.version'] = '{project-version}'
 
 dependencies {
     implementation 'org.springframework.kafka:spring-kafka'