chore(copilot): use GH_HOST for Copilot endpoints and token lookup

[rmuir]

Update Copilot HTTP requests and token lookup to respect the GH_HOST env var, allowing use with GitHub Enterprise instances.

Some networks block the github.com endpoints, so they won't work at all. Provide a way for the user to hit different endpoint other than github.com (e.g. mycorp.ghe.com) without patching the source code.

The GH_HOST environment variable is the same one used to override this for gh cli: https://cli.github.com/manual/gh_help_environment

Note: maybe this isn't the best solution, I'm not a lua guy... but I tested it in such a restrictive environment and it works.

[rmuir]

Maybe a cleaner solution would be to parse out of the oauth rather than looking for github.com, I don't know. ~/.config/github-copilot/apps.json entry looks like this, the mycorp.ghe.com is in there. Could be a better solution than environment variables and "just work" in more cases:

{"mycorp.ghe.com:Xy1.00deadbeef0":{"user":"my-user","oauth_token":"<nope>","githubAppId":"Xy1.00deadbeef0"}}

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[AmadeusK525]

@olimorris Any chance this could be merged? My company just updated copilot support to use Enterprise, so I can't use CodeCompanion anymore without this PR

[AmadeusK525]

Well, I don't think this patch is enough... testing it locally I can see that the way the plugin handles URLs is too coupled, as the URL is always fully formed with host + path. The "real" fix would be to separate this

[olimorris]

All - apologies for not getting to this sooner. @rmuir presume this is good to be merged?

Aware this isn't enough for @AmadeusK525 but potentially still useful for other users.

[rmuir]

@olimorris I think it is no good for current main. I tried this PR after the merge to latest in my restrictive environment and PR seems to have problems. When sending an actual chat, I see error implying it is still trying to connect to github.com and hitting firewall:

[chat::_submit_http] Error: { "curl: (35) Recv failure: Connection reset by peer" }

[AmadeusK525]

Hey, I re-opened this in #2705, and it does work (I've been using it for a while)