Feature request: add -i INPUT.json, --input INPUT.json option to miniwdl check

[TedBrookings]

One common source of errors in development is errors in input JSONs. It would be nice to be able to pass an input JSON to miniwdl check to ensure that it's compatible. Depending on how miniwdl run is being invoked it can take awhile and consume cloud resources just to discover that an input file doesn't exist or an input had a typo in the variable name.