Add Configuration Option for Network Proxy in Copilot CLI

[iwangbowen]

Currently, Copilot CLI does not provide a built-in way for users to configure network proxy settings, which can be problematic in environments requiring proxy access for internet connectivity. Introducing a configurable proxy option, such as through command-line flags or a configuration file, would allow users to specify proxy details (e.g., host, port, authentication) seamlessly. This enhancement would improve usability in corporate or restricted network setups, enabling smoother integration and reducing manual workarounds. Implementation could follow standard CLI patterns, like adding --proxy flags or a proxy section in a config file.

[lukefx]

It would be perfect if copilot cli could respect HTTP_PROXY and HTTPS_PROXY (or ALL_PROXY) env vars. Currently we cannot use it in our company since we cannot reach the internet without proxy.

[devm33]

De-duplicating with #41

See #41 (comment) for latest update