Add support for private KnServices

[duglin]

In what area(s)?

/kind good-first-issue
/kind feature
/kind proposal

Describe the feature:

It would be nice if there was a way to specify that a knService should not have an external endpoint. This means setting the label serving.knative.dev/visibility: cluster-local.

[rhuss]

Good point. I suggest introducing an option --cluster-local and --no-cluster-local.

[rhuss]

The handling could be similar like for --concurrency-target

[maximilien]

/assign @maximilien

[maximilien]

@duglin you OK with @rhuss suggested flags? Seems reasonable to me.

[maximilien]

Also, I am assuming this is both at create and update of a service.

[duglin]

yep sounds good on both questions