Improved exception content (invalid field)

[osteel]

Description

This PR appends the invalid field when the validation error is a schema mismatch.

Motivation and context

Current exceptions miss this information, making tracking the error more difficult.

How has this been tested?

With a real scenario and the ValidationExceptionTest class has been completed.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.