When K_SINK is not defined, Kogito Knative Eventing application fails to run

The `K_SINK` variable must be in the environment for Kogito applications using the Knative Eventing add-on. Otherwise, it will fail on bootstrap. Ideally, the application should start OK, and WARN the user and return a "not ready" status to the probe if the variable is not yet present. The Knative platform will eventually inject this variable.