Updating a function does not create a new knative kservice revision

[yairyairyair]

Sorry for submitting a lot of bugs and feature requests lately. (impressed by this project)

Anyway when updating a knative service it has a whole revisions system and traffic control for canary deploys and a lot of functionality.

This is not possible when adding open function, because when updating a function yaml and re-apply it destroys the old function and old knative service, it should simply update the knative service and allow knative to do the revisions stuff and routes stuff itself so we can allow canary deploys.