docs: add reviewedAt field to gated repo access report documentation (#2470)
Document the new `reviewedAt` timestamp field added to the access request
download report and API responses, which indicates when a request was
accepted or rejected.
Co-authored-by: huggingface-doc-bot <doc-bot@huggingface.co>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>