Document that spring.jmx.enabled is not for third-party libraries

Closes gh-42272

Author: philwebb

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jmx/JmxProperties.java

@@ -29,7 +29,7 @@
 public class JmxProperties {
 
 	/**
-	 * Expose management beans to the JMX domain.
+	 * Expose Spring's management beans to the JMX domain.
 	 */
 	private boolean enabled = false;
 

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/jmx.adoc

@@ -9,6 +9,9 @@ Any of your beans that are annotated with Spring JMX annotations (`@ManagedResou
 If your platform provides a standard `MBeanServer`, Spring Boot uses that and defaults to the VM `MBeanServer`, if necessary.
 If all that fails, a new `MBeanServer` is created.
 
+NOTE: `spring.jmx.enabled` affects only the management beans provided by Spring.
+Enabling management beans provided by other libraries (for example Log4j2 or Quartz) is independent.
+
 See the {spring-boot-autoconfigure-module-code}/jmx/JmxAutoConfiguration.java[`JmxAutoConfiguration`] class for more details.
 
 By default, Spring Boot also exposes management endpoints as JMX MBeans under the `org.springframework.boot` domain.