Make queue java 11

This upgrades the current spring version to the newest version 2.1.7.

With this spring security was also updated and therefore some changes were made to the authentication system in the Queue.

Furthermore, the CI/CD has been changed slightly. I have specified the java version for buildpacks in the file system.propertiesas otherwise it would fallback to java 1.8 by default.

src/main/java/nl/tudelft/ewi/queue/dialect/AuthenticatedExpressionObjectFactory.java

@@ -65,7 +65,7 @@ public class AuthenticatedExpressionObjectFactory implements IExpressionObjectFa
 		if (authentication.getPrincipal() instanceof UserPrincipal) {
 			UserPrincipal userPrincipal = (UserPrincipal) authentication.getPrincipal();
 
-			return userRepository.findById(userPrincipal.getUser().getId());
+			return userRepository.findById(userPrincipal.getUser().getId()).orElseThrow();
 		}
 
 		return authentication.getPrincipal();