Use cli for managing workspaces instead of the API

We have to re-implement logic (like shutting down a workspace before updating it) and it would be better to just call out to the cli since it already accounts for all that.

It is a lot of surface area to cover (every plugin) any time a feature is added.

If the command errors, show whatever is in stderr as the error message.

An alternative would be to handle these things at the API layer, and maybe there is a case to be made for that.