[incubator-kie-issues#1249] Fix REST call in process-rest-workitem-quarkus example

[martinweiler]

Fixes https://github.com/apache/incubator-kie-issues/issues/1249

Some points regarding the changes to fix this example:

• Port needed to change from 80 to 8080 (added parameter in the WIH of the process)
• The previous version of the example used Quarkus REST Client, this would have required a config change
• With the REST client approach, the REST call was targeting https://petstore.swagger.io/v2/user/{user}. This call might have returned 200 for a demo user in the past, but now always returns 404. This makes it unusable for the example.
• To simplify the example, I replaced the usage of the REST Client using petstore with a simple REST service within the application.

[LightGuard]

Thanks for the fix, @martinweiler!