Build a Windows Service that implements CoderVPN

[spikecurtis]

Create a native Windows Service that auto-starts with Windows and creates a named pipe to accept connections from the user application.

On connection, it uses the CoderVPN protocol (#3) to communicate with the user application. When the user application starts the VPN, it uses the provided credentials to connect to the Coder deployment, download the Coder binary, create a pair of communication pipes, then fork/exec to start the coder daemon process (coder/coder#14735).