Verify lua script compilation as part of config validation

[binarylogic]

This would be a nice a touch for the lua transform, to ensure the lua script passed is syntactically valid. We can't verify execution because we won't know the structure of the event, but we can verify syntax.

There's a chance we already do this. If that's the case, please close.

I'm thinking about slightly changing the execution model, so that the script source would be used to create a transformer function at start and then execute it for each transform. This should both improve the performance and do the parsing at the step when the transform is initialized.