Add option for JSON output

> we should perhaps look at a JSON output option.

I agree - I don't think people should consider the `--check` output as stable enough to parse, at least right now.

> I want to create an automated workflow that does the following nightly

It'd be great if we can support this kind of workflow.

_Originally posted by @ee7 in https://github.com/exercism/canonical-data-syncer/issues/61#issuecomment-713669969_