--fail-on as list instead of formatted string

[mbalatsko]

Current solution: --fail-on takes ;-separated string of all licenses to fail on. And if you want to restric all unfree licences it will be really looking string.

Idea: Make it accept list of strings. It would look better both in CLI and in pyproject.toml config.

Also we can make a shortcut, e.g. --fail-on-unfree and cherry pick list of unfree licences from https://github.com/NixOS/nixpkgs/blob/master/lib/licenses.nix, which is. really well maintained