gh cs list: add a way to extract the currently bound SSH port

### Describe the feature or problem you’d like to solve

I want to set up my Codespace using Ansible. (The default dotfiles setup does not meet my needs.) However, Ansible is designed to take a hostname and port, so I cannot use `gh cs ssh`. (`gh cs ssh` also prints unwanted status messages to stderr, which would interfere with my playbook even if I could use it.)

Right now, I have to mount it with `gh cs ssh`, find the bound port with `sudo netstat -tapn`, and then use that port with my Ansible playbook.

### Proposed solution

It's easy enough to mount the port with `gh cs ssh -c CODESPACE-NAME -- -N 2>/dev/null &`, but I still need to find the port. If `gh cs list` had some way to list the currently bound port so I can retrieve it later with just the codespace name (e.g., with `--json`), then I could extract it and script the entire setup process whenever I create a new codespace.

I realize that I could specify a specific port, but that isn't quite sufficient, since I'd still like to use `gh cs list` to extract the data in, for example, some Vimscript, and it's a lot less convenient to have to preserve the port and reuse it elsewhere than to just look it up in the Vimscript.

### Additional context

If you're happy with the design, I'm happy to implement it.