Extend `Logged in with gh` to support GHE

[andyfeller]

Describe the feature or problem you'd like to solve

As a GHE user, I would like copilot to leverage my ghe.com session from gh like it does when I'm authenticated with my github.com session

Proposed solution

As a GitHub CLI user, I am authenticated with both GitHub.com and GHE accounts. gh determines the appropriate credentials based on various factors:

1. Local git repository remotes
2. Command line arguments that capture HOST/OWNER/REPO
3. GH_HOST env var

The benefit is a uniform streamline experience for both GitHub Copilot CLI and GitHub CLI users.

Example prompts or workflows

No response

Additional context

When I launch copilot authenticated to github.com:

When I launch copilot authenticated to GHE tenant:

[andyfeller]

Please let me say I know this is a little complicated especially with multi-account support across the 2 CLIs. In gh when multiple hosts are authenticated, it defaults to github.com unless 1) the local git repository remotes point elsewhere, 2) some --hostname flag, or 3) GH_HOST env var is set.

That last option might be an okay short term solution: copilot could inspect and leverage GH_HOST to decide which gh session to use for copilot auth. 🤷