feat: add json formatted output option

It's become somewhat popular to include JSON output as an option, to make it easier to combine multiple utilities reliably. Examples include the `iproute` utilities (e.g., `ip --json addr`) and `systemd` utilities (e.g., `systemctl list-units -o json`). Structured data is a very powerful technique for organizing scripts -- so much so that shells are being created built around the concept (e.g., Nushell).