feature: create blank/template input JSONs

[a-frantz]

The workflow for using this feature would look something like:

sprocket inputs quality-check.wdl > qc-inputs.json
vim qc-inputs.json
sprocket run --input qc-inputs.json quality-check.wdl

There are some considerations to make before implementing. Are the output JSONs filled in with anything? Or blank? How to handle nested inputs? Inputs with default values? etc.