* feature(source cronjobs): Implementation of CronJobSource management
Contains create/delete/update/describe but not tests yet.
Still todo:
* Think how to provide a namespace for the sink
* Support for more sinks
* Synchronous mode for create & update
* Add list (or implement "source list")
* chore: Add a mock test for cronjob source
* addd missing license headers
* cosmetic changes
* chore(cronjobsource): Add tests
* fixup
* chore(cronjob source): Improved test coverage
* chore(cronjob source): some review polishing