Enable environment for storage of listener variables

[slalomsk8er]

Is your feature request related to a problem? Please describe.
Command line arguments aren't save as they show up in process lists and look ugly and unwieldy if multiple listeners are used.
Also a extra file can help avoiding to commit security tokens and specific instance information into version control.

Describe the solution you'd like
In my own listeners I also get the variables from the environment in addition to arguments passed on the command line.
For security tokens I additionally utilize the Robocorp vault.

This helps with utilizing the Robocorp rcc as robot framework runtime and the Robocorp extension for VSCode for robot framework development.

Describe alternatives you've considered

• being lazy and just pass the variables on the command line
• create a fork and maybe a pull request

Additional context
https://robocorp.com/docs/development-guide/variables-and-secrets/configuring-robots-using-environment-variables