Tunnel invocations should connect to running tunnels

[aeschli]

There should only be one tunnel server running at a time. So when code tunnel is called a second time it should discover the running server and exit again with a success message.

-> Needs a new command to code tunnel stop to stop already running services.

[connor4312]

This is implemented now

[connor4312]

Verification:

• Grab the latest standalone CLI https://code.visualstudio.com/insiders/
• Open at least two terminals, and don't have remote tunnel access turned on in VS Code (or have VS Code closed)
• Run ./code-insiders tunnel --verbose in terminal.
• Verify starting as new singleton is printed in the terminal and the tunnel starts
• Run ./code-insiders tunnel --verbose in another terminal
• Verify it prints "Connected to an existing tunnel process running on this machine." with control instructions after replaying recent logs from the singleton
• Verify the control commands printed work as expected
• Have the two tunnels running again. Ctrl+C in the singleton terminal. Verify the previous "client" terminal notices that and starts up the tunnel
• Verify the commands code tunnel status, code tunnel restart, and code tunnel kill work. These are alternatives to the "interactive" commands clients normally print. status should exit with an error if no tunnel is running.