Return first handshake uriScheme in unauthenticated route

[Cerchie]

We're getting a lot of "TypeError: fetch failed" alerts from Sentry.

From Dave Shoup (@shouples):

the first thing that comes to mind is the sidecar keeping track of the uriScheme that did the first handshake, and maybe we can have an unauthenticated route that returns whatever that value is? for example, if a user starts the extension in VS Code and then jumps over to VS Code Insiders, Insiders will fight to handshake and get 401s (until the sidecar process is killed and the handshake completes)