Kerberos proxy support

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

Certain proxies require Kerberos support. Without this being supported in the CLI, users requiring this type of auth are unable to use the tool.

### Proposed solution

Allow the CLI to have kerberos support to enable authentication further down the chain, i.e. firewall/proxy auth in corporate network.

### Example prompts or workflows

_No response_

### Additional context

https://github.com/github/copilot-cli/issues/41#issuecomment-3485585879