migrate https://github.com/crw-samples/rest-http-example/tree/devspaces-3-rhel-8 to JDK 11

In DS 3.0, there is only ONE remaining project that uses JDK 8: maven-spring-boot-http-booster -> rest-http-example

We also have a couple remaining references to java8:

• https://github.com/crw-samples/jboss-eap-quickstarts/blob/devspaces-3-rhel-8/kitchensink-jsp/crw-java8-maven-eap.yaml#L18 (devfile v1 / obsolete)
• https://github.com/redhat-developer/devspaces/blob/devspaces-3-rhel-8/dependencies/che-devfile-registry/devfiles/00_java11-maven-eap/devfile.yaml#L17 (devfile v1 / typo)

So the task here would be to:

• remove obsolete refs to JDK 8 in projects that have moved to JDK 11;
• update rest-http-example project to use JDK 11;
• set JDK 11 as the default JDK in UDI, with option to use JDK 8 if needed (customer devfiles, not our samples)