Save the credentials after first login on CLI agent

[aritroCoder]

Although it saves the credentials for the GUI version, the CLI lacks the saved credentials capability which is an hinderence and should be fixed.

[yuezk]

In 2.3.7, you can save the credentials get from gpauth <portal> to a file and pipe it to the gpclient with sudo gpclient connect <portal> --cookie-on-stdin.