Add timeout support

[holmboe]

It would be nice to be able to specify a timeout for the question and if no user input was provided it would continue using a default.

The use-case is: I want to allow a human operator the possiblity to change some variables at runtime, and at the same time allow the playbook to be runnable with defaults in order to use them with CI/CD pipelines.

[andrewvaughan]

I like the idea - it helps drive the headless deploy idea. I'll prioritize this and see when I can get it out.