JSON schema validation for test runner output

While working on the Java test runner I had the idea that it might be useful to automatically validate the JSON output of the test runner against a schema derived from the test runner interface documentation.

To my knowledge nothing of the sort is available yet, so I was wondering whether it makes sense to add this somewhere. All test runner repositories could then add a step in their CI workflows that validate the output they generate.

CC @ErikSchierboom :wink: