Improve documentation for JMX related keys

Closes gh-2747

spring-boot-actuator/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -17,6 +17,12 @@
     "sourceType": "org.springframework.boot.actuate.endpoint.EnvironmentEndpoint",
     "description": "Keys that should be sanitized. Keys can be simple strings that the property ends with or regex expressions."
   },
+  {
+    "name": "endpoints.jmx.enabled",
+    "type": "java.lang.Boolean",
+    "description": "Enable JMX export of all endpoints.",
+    "defaultValue": true
+  },
   {
     "name": "info",
     "type": "java.util.Map<java.lang.String,java.lang.Object>",