Add support for "promptFilePath"

[Junkern]

Not sure if that fits this projects goals, but I came across several use cases where I prompt the user to input a "filePath" string (aka /Users/some/path) which I need for other scripts.

I always have to check whether this paths exists, and if not, basically reprompt the user. It would be cool to have this built in into cli-ux.

Not sure exactly how, maybe as an option for promt ( filePath: true?). I would also be happy to supply a PR and tests.