Determine if ytt schema errors are user friendly in context of kapp-controller

One question that came up in the Carvel community meeting is what ytt schema errors look like when seen via a PackageInstall/App status. We do not currently have any testing in place for ytt schemas with kapp-controller so it might be worthwhile to add error case tests to assess if the UX is consumable for users. It would also be helpful to manually view statuses to assess if the information is easy to follow when errors happen.

More on schemas in docs here: https://carvel.dev/ytt/docs/latest/how-to-write-schema/#docs

One particular issue I was wondering about is what if there are many schema validation errors? Would all of that information be overwhelming to users?

## Acceptance Criteria
1. A brief summary of the UX with any proposed changes that we should consider.
2. If the changes are small, feel free to implement them as part of this story. If the changes are large, please create an issue so that we can schedule the work.

Start with the ytt schema documentation and any existing PackageInstall or App status tests in kapp-controller. Create schema-validation error cases, inspect the resulting statuses manually, and record whether multiple errors are understandable. Done means a brief UX summary with proposed changes, plus small fixes if appropriate or a follow-up issue for larger work.

Written by the indexing model from the issue text.