Allow login from different machine

[ulrichSchreiner]

When working with different systems it would be great to login without having direct access to a window environment on the target system. The current implementation starts a local browser with a message like

Opening Browser for Authentication. If this does not work, please point your browser to http://localhost:45809

The given link can only be opened on the system where the cloudctl login was executed.

I would propose a legal internet link, so for example one can login via SSH to the remote system and invoke a login:

cloudctl login
please point your browser to https://login.example.com/app/458097898287

The user can copy this login-link to any system with a regular browser, open the link, do the login and when this succeeds, the blocked cloudctl process returns and writes the token.

At the moment one can use https://github.com/ekzhang/bore to tunnel the port but this is a real bad user experience as the login page does redirects to localhost.

To get a feeling of the login procedure simply use tailscale login which shows an URL which can be copied to any other system. So one can invoke the login on a headless server while doing the real browser login on a local machine with a desktop environment.