Currently the implementation of KieServerController getController() in KieServerImpl uses the default, or the first class loaded through the ServiceLoader. This makes it difficult to override, especially as the WebSocket implementation is usually present.

This change allows multiple implementations to exist, and when they do, they are checked to see if they are supported, and are of a higher priority. The default is not instantiated automatically as this is always available to the ServiceLoader.

This change is designed to mirror the KieServicesClientProvider. However, the change could not be applied to the KieServerController interface as that is also used elsewhere in the kie-server (for example org.kie.server.controller.websocket.WebSocketKieServerControllerImpl)