Support environment variables for credentials

[haraldmeyer]

It would be good if the tools supported the standard environment variables to provide username, password, and tenant. This would help keep the commands short, would not compromise credentials in screensharing and would enable the usage of the session management feature of the c8ycli command line tool (https://goc8ycli.netlify.app/docs/gettingstarted/)

[skom-c8y]

This is tracked internally via PAB-4502