fix(document_extractor): pptx file type and missing metadata_filename UnstructuredIO

[hgbdev]

Summary

The issue occurs when two environment variables for UnstructuredIO, UNSTRUCTURED_API_URL and UNSTRUCTURED_API_KEY, have been defined.

After uploading a PPTX file and processing it through the Doc Extractor (UnstructuredIO), an error message appears: "If file is specified in partition_via_api, metadata_filename must be specified as well."

I checked and noticed that the file type might not be correctly set for the partition_via_api method when handling .pptx files. Additionally, I added the metadata_filename, which was previously missing, to extract the value from the file name.

References from the unstructured package:
• Line 54
• Line 107

Screenshots

Before:	After:

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods