Add --pretty option to "secret inspect" and "config inspect"

[aaronlehmann]

Other "inspect" subcommands have a --pretty option. secret inspect and config inspect appear to be missing it. This is important because otherwise there's no human-readable way to get information about a config or secret object. It's particularly necessary for config inspect so the config payload can be exposed in cleartext, instead of the base64-encoded form that gets spit out over the JSON API.

cc @dhiltgen