Add GH action: convert yaml to json

[radishmouse]

Closes #3 Closes #8

This PR:

• Runs the yaml to json conversion
• Validates existing json and any new json produced by the conversion
• If all json is valid, commit new json to repo

Changes to the validate workflow were necessary since it is called from the convert workflow:

• Makes the validate workflow reusable, but retains standalone functionality
• Adds inputs and outputs to validate
  • the should_download input tells validate to download the JSON artifacts produced during the GH action
  • the is_valid output contains the status of the validation (whether all json files were valid)
• Per feedback, a python script now wraps the JSON validation command line tool

Tested locally using nektos/act:

• act pull_request simulates a PR
  • This tests the validate workflow in standalone mode
• act push --artifact-server-path /tmp simulates a push
  • This is for testing the convert workflow (which calls validate before attempting to commit)

Note: only partially tested on GitHub. (This PR includes an example JSON file that passes validation.) #13 has been created to address this.

[radishmouse]

One thing that's missing is that the resulting json files need to be commited/pushed to the repo. I'll update the GH action to include those steps

[radishmouse]

@malini I have tested this code heavily locally, but not on GitHub.

I have created #13 for testing on GH, but would feel more comfortable with at least one more set of eyes on the workflow code before I merge.

[radishmouse]

@MelissaAutumn I've added a python wrapper script for validation and moved the checks for yaml & json files from the workflow file to python. When you get a chance, please take a look?