In the v1 CLI, guide users to v2 if using unknown subcommands

[nluaces]

Is your feature request related to a problem? Please describe. In the v1 CLI, guide users to v2 if using unknown subcommands

Describe the solution you'd like

Suggested extra text:

$ skupper site
Error: unknown command "site" for "skupper"
Run 'skupper --help' for usage.

Note that this is the 1.x Skupper CLI.  Get the 2.x CLI if you are using the 2.x docs and examples.