States*DiscoverCmd should be able to show progress bars

[azriel91]

StatesCurrent and StatesDesired discovery can take a while to execute.

• It should be possible to show progress bars when these commands are executed.
• It should be possible to not show progress bars as well, because some discovery may be fast (e.g. if it is all local).

Because ApplyOpSpec does state current and state desired discovery, this will result in the progress bar needing to be filled from 0 to full, three times.

This issue does not cover layered progress bar styling where we have a "state current progress layer", "state desired progress layer", and "apply layer".