Add option for env var to bypass certificate checks

In reference to https://github.com/cli/cli/issues/1735

Many organizations use TLS Inspection for security purposes on internet traffic. Currently there is no way in `gh` or other commands relying on `go-gh`. As per this comment from @babakks - https://github.com/cli/cli/issues/1735#issuecomment-3167529911 - any solution with env vars would need to happen in `go-gh` rather than `gh cli`

I noticed that no issue had been created here and there was no additional follow up on the issue in the cli repo. Hoping to get this pushed forward, as some organizations will be unwilling to allow bypassing inspection at the firewall.