improve error discovery for missing data values

> Error message:

```
Stderr: kapp: Error: Validation errors:
- Expected 'kind' on resource '/ () cluster' to be non-empty (stdin doc 10)
- Expected 'apiVersion' on resource '/ () cluster' to be non-empty (stdin doc 10)
- Expected 'metadata.name' on resource '/ () cluster' to be non-empty (stdin doc 10)
```

> Okay, this took a long time and was pretty much trial and error, would love to find some way to possibly make that easier. My secret that I was using for inline.pathsFrom with the ytt section didn't have #@data/values at the top.

how do we improve finding this kind of error? will schemas help with this?