This implements a new command "config" in the CLI to handle RevPi
configuration. It includes parsing and subparser setup for
configuration-related operations. The change improves usability by
extending CLI functionality to manage RevPi configuration objects.
Introduce a new 'list-features' action to display all available features
via CLI. Updated argument handling to make 'feature' optional for
'list-features' and added a validation step to ensure the feature name
is provided for other actions.
This function facilitates retrieving specific properties from a DBus
interface, improving code modularity and reusability. It supports both
system and session bus types, streamlining access to DBus resources.
