Add @EndpointServlet and migrate Jolokia

Add first class support for Servlet based endpoints and rework the
Jolokia endpoint to use it.

Fixes gh-10264

spring-boot-samples/spring-boot-sample-actuator-ui/src/main/resources/application.properties

@@ -2,4 +2,3 @@ spring.security.user.name=user
 spring.security.user.password=password
 management.health.diskspace.enabled=false
 management.endpoints.web.expose=*
-management.jolokia.enabled=true