Handle nested files for AOAI graders

[ebwinters]

Description

PR handles nested files for AOAI graders. There were previously bugs in generating the data_source_config and data_source correctly when creating AOAI shadow runs. The PR fixes these by handling the item wrapper correctly, creating dataset columns for nested data correctly, and handling the sample key word by keeping it separate from item.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

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