Human-readable bootc status

[lukewarmtemp]

Fixes #408

[cgwalters]

Thanks for working on this! I need to pull your PR and try it but just at a quick look, it's just a shorter YAML serialization right?

I had been thinking we'd output something more like rpm-ostree status that is explicitly not parsable by machines, just intended solely for human visual consumption. Other prior art is e.g. systemctl status which is partially structured but also uses ASCII art drawing characters, etc.

Before we try to write too much more code I think it'd be good to have a bike shed (maybe in the original issue) with some proposed example outputs that different people would like to see from this. Does that makes sense?

[cgwalters]

I think we can probably just go ahead and default to human-readable if we're writing to a tty by default.

That avoids the need to call it anything at all, and avoids "typing fatigue" from a potentially frequently used CLI option.

Arguably then, we could also simultaneously switch to JSON by default if we're not on a tty.

But, we probably do need a general option here like:

enum OutputFormat {
  HumanReadable,
  YAML,
  JSON
}

or so and

pub(crate) format Option<OutputFormat>

or so.

[cgwalters]

#639