Add output format flag

Introduce a output flag to provide structured output that is more suitable for programmatic usage of command output. To be familiar to Workflow users this should be similar to the `kubectl` implementation: `-o=`. Using `-o=json` should result in returning the JSON data directly from the REST API for the Controller. It might be nice to also provide YAML output (again for familiarity of `kubectl` users), but providing JSON alone may be sufficient.