Add paths command for listing all output paths for a release

[lucperkins]

The paths command enables you to list all output paths for a flake release as nested JSON. Here's an example:

fh paths "my-org/nixos-configs/0.1"

{
  "nixosConfigurations": {
    "prod-server": "/nix/store/j8mdgrcb91778ywx7jfxax14ly8ypynz-prod-server"
  }
}

[grahamc]

Some hesitations/questions I'm having:

1. This makes the version of org/flake/version optional, with a default to *. I think we should make sure we like this syntax and do a bit of internal vibe check. Let's chat at standup?
2. paths is a bit of a weird name for this command. Maybe outputs? Is there a noun verb structure we can put in place house this?

Separately, I think this is a good PR. Especially for debugging why fh resolve is grumpy at me ...