Add cli options to get the dart / flutter sdk paths

[benthillerkus]

The VS Code Dart extension recently got this new feature Dart-Code/Dart-Code#5377

It'd be nice if puro had some cli options that would output the path, so that I could set these globally in my user profile and then I think changing the settings.json wouldn't be required anymore

[pingbird]

this should be simple enough to add

[RKartashov]

This would actualy help me with some autamation in a project at work