That’s just a URL that happens to return your Postman Collection as a JSON response. The URL could be anything that returns that known format doesn’t need to be Postman specific.
You’re dealing with a node script there and using that syntax just wouldn’t work that way.
It would be the same as if the node script did something else completely different that was nothing to do with Postman.
You can hardcode the value, store it as a variable, use something like the dotenv module as a config file, read the value from a system environment file but you can’t directly look into the JSON file in the same way.
You could read the JSON file with fs and extract out those values with vanilla JS but you can’t use {{..}} in the URL link because it would just be sending that complete string as the URL.
If you have feature requests and issues relating to the documentation, I would encourage you to raise them against the Newman repo so we can action those in the right place.