Fix Path Traversal issue

[jxfzzzt]

Describe the bug

Hello, i find a issue in src/libre_chat/router.py, there may be a path Traversal vulnerability in method upload_documents.
if the filename of a uploaded in files be /../../../../../../../test.txt (e.g., modified by Burp), it may lead to a vulnerability that allows arbitrary file writes. #9

Reproduction

filename of a uploaded in files be /../../../../../../../test.txt

Operating System

Linux, Mac, ...

Libre Chat version

0.0.6

Additional context

No response

[jxfzzzt]

@vemonet Could you please take a look at this issue?