Provide example payloads for all swagger endpoints

There are some endpoints which includes example payloads, such as:

https://github.com/kiegroup/droolsjbpm-integration/blob/master/kie-server-parent/kie-server-remote/kie-server-rest/kie-server-rest-case-mgmt/src/main/java/org/kie/server/remote/rest/casemgmt/CaseResource.java#L168

There are some where such example does not exist:

 https://github.com/kiegroup/droolsjbpm-integration/blob/master/kie-server-parent/kie-server-remote/kie-server-rest/kie-server-rest-dmn/src/main/java/org/kie/server/remote/rest/dmn/ModelEvaluatorResource.java#L104

 Let's add example payloads to all endpoints where it make sense. These example doesn't need to be container specific (this is not related to BAPL-1787 in any way)- just a generic json/xml which would make it slightly easier for developers consume those endpoints would be enough.