Create helper command to build configuration file

[davidban77]

On a new installation of labby the configuration file is not present. It would be good to create a helper command to create a basic configuration file.

Basically to cover:

• A series of prompts asking for details like name of the environment, GNS3 server to connect, and so on...
• Some disclaimers hinting to create a configuration file, or to run the helper command if the file is not present.
• Some disclaimers around environment variables and setup to handle secrets.