Change --skip-instance to default to true

[simonvane]

What would you like to be added:
Change the default of --skip-instance used in kubectl-kudo install [flags] to be false.

Why is this needed:
It is really easy to forget to add the --skip-instance flag when running the install command. It is surprising (to me at least) to get an instance created automatically. This can incur significant costs depending on what is being deployed by the operator.