cdk migrate cli UX issue

When not supplying stack name an error with unclear messaging is shown. Expectation state the missing parameters

```
$ ./node_modules/cdk/bin/cdk migrate --from-path template.yaml --output-path cdkstack/
❌ Migrate failed for undefined: stack generation failed due to error
'The text and separator arguments should be of type string'
```

supplying --stack-name test as well resolves the issue but it was unclear that this was needed from the error.

Reproduce the issue with the shown cdk migrate command, first without --stack-name and then with it. Inspect the migrate CLI handling of the required stack name; done means the missing parameter is identified clearly instead of producing the current undefined and type error message.

Written by the indexing model from the issue text.