example hook: dataset metadata validation

[ozkatz]

This PR also adds:

1. basic stacktraces to lua hooks, which in most cases is just the line numbers of where things fail, as the call stack is pretty shallow. You try writing a >100 line lua script without this!
2. The ability to separate errors from explicit failures, and present the latter in a friendlier way to the user

[github-actions[bot]]

E2E Test Results - DynamoDB Local - Local Block Adapter

[github-actions[bot]]

:recycle: PR Preview 2aea483e42e421e5cf93f5e7f324322284924a7f has been successfully destroyed since this PR has been closed.

_{🤖 By surge-preview}

[ozkatz]

@N-o-Z PTAL :)