Fix for Issue #616: Handle Ingestion of Documents with Uppercase Extensions

[fshnkarimi]

Hello,

I've addressed the issue #616 regarding the problem faced when ingesting documents with uppercase file extensions. Here's a breakdown of my changes:

Modified the load_documents function: now, files with uppercase extensions are renamed to have lowercase extensions before processing.
This ensures that documents, regardless of their original extension case, are ingested consistently and without issues.
Checked that all changes are in compliance with the pre-commit hooks and confirmed they pass all checks.
By making file extensions uniformly lowercase, we should now be able to ingest documents without facing issues related to varied extension casing.

Please review my pull request, and I'd appreciate any feedback or suggestions for further refinement.

Thank you for the opportunity to contribute!

Warm regards,
Afshin Karimi

[LeafmanZ]

works well