[KSW-Guides][Operator] Add a new section under "operator" to explain how the operator expose workflow services in devmode

This new section should explain how the operator operates in dev vs prod mode. That in prod is up to the user to define.

Additionally, since we will deploy it as a Knative Serving in dev, we can rely on it for URI exposition in the near future. For now, explaining that users should expose the services by themselves in prod should be enough.