Add jaxb and javax.assist dependency for enabling guestbook-service to be executed in java 11

[ArkaBando]

Please add these dependencies for java 11 support , Faced compilation error while goining through https://www.coursera.org/learn/google-cloud-java-spring/home/welcome course since gcloud instances default jdk version is 11.
dependency>
javassist
javassist
3.12.1.GA

javax.xml.bind jaxb-api 2.3.0 com.sun.xml.bind jaxb-core 2.3.0 com.sun.xml.bind jaxb-impl 2.3.0