There are some missing environment variables in `copilot help environment`

### Describe the bug

When I run `copilot help environment`, the content displayed is incomplete. I can see the full version [here](https://docs.github.com/en/copilot/reference/copilot-cli-reference/cli-command-reference#environment-variables), and I hope it can be added to the `copilot help environment` command output.

### Affected version

GitHub Copilot CLI 1.0.40.

### Steps to reproduce the behavior

1. `copilot help environment`

### Expected behavior

I expected that all environment variables, including experimental settings, would be displayed in the `copilot help environment` output.

### Additional context

_No response_

Start by locating the implementation of the `copilot help environment` command and compare its output with the linked CLI reference. Update the command's environment-variable listing to include the missing and experimental settings, then run `copilot help environment` to verify that the displayed list matches the reference.

索引モデルが issue の本文から書いたものです。