* Attempt to use Electron fetch for github-authentication
Also changes fallback from node-fetch to the built-in Node fetch
* Remove Content-Length header Electron compatibility
It looks like it was set incorrectly to the body contents anyways.
The flows are crucial to the extension and I wanted to be able to declare which can be used when in a declarative way. This reworks the flows into that model.
Additionally, it pulls in the Client ID and secret from a config which will allow us to not rely on the vscode.dev proxy on Desktop (because we can make a distro change that includes the secret... which isn't a real secret, says GitHub)... unfortunately we still need to rely on it for Web due to CORS but we're in a position where it will be easy to rip the proxy out when GH supports it.
