Document how to exclude an annotation processor with Maven

See gh-22000

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -7583,15 +7583,42 @@ If you do it that way, the library is not provided and, by default, Spring Boot
 
 Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (`META-INF/spring-autoconfigure-metadata.properties`).
 If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time.
-It is recommended to add the following dependency in a module that contains auto-configurations:
+It is recommended to add the following dependency in a module that contains auto-configurations and exclude it in the `spring-boot-maven-plugin` to prevent the repacking task from adding the dependency into the fat jar:
 
 [source,xml,indent=0,subs="verbatim,quotes,attributes"]
 ----
-	<dependency>
-		<groupId>org.springframework.boot</groupId>
-		<artifactId>spring-boot-autoconfigure-processor</artifactId>
-		<optional>true</optional>
-	</dependency>
+	<project>
+    ...
+    <dependencies>
+      <dependency>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-autoconfigure-processor</artifactId>
+      </dependency>
+    </dependencies>
+    <build>
+      ...
+      <plugins>
+        ...
+        <plugin>
+          <groupId>org.springframework.boot</groupId>
+          <artifactId>spring-boot-maven-plugin</artifactId>
+          <configuration>
+            <excludes>
+              ...
+              <exclude>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-autoconfigure-processor</artifactId>
+              </exclude>
+            </excludes>
+          </configuration>
+          ...
+        </plugin>
+        ...
+      </plugins>
+      ...
+    </build>
+    ...
+  </project>
 ----
 
 With Gradle 4.5 and earlier, the dependency should be declared in the `compileOnly` configuration, as shown in the following example: