"Validate only" mode for system tests #272
Description
Would be nice for users to be able to validate the YAML files in a test suite, ensuring:
- suite files are valid, and all inputs & expectations exist.
- inputs / seeds are valid, including topic records' keys and values match expected types and any associated schemas.
- expectations are valid, including topic record's keys and values (partially) match expected types and any associated schemas.
All without running the tests themsevles.