Add support for PDF file uploads as context for LLM queries

[andrewwan0131]

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Why are these changes needed?

These changes enable users to upload PDF files as context for LLM queries.

Changes made

1. Added PDF file handling capabilities:

   • Implemented PDF file upload support in the web interface
   • Added PDF text extraction functionality
   • Integrated extracted PDF content as context for LLM queries

2. Modified relevant files:

   • Updated gradio web server components to handle PDF uploads
   • Added PDF processing utilities
   • Enhanced chat protocol to include document context

Checks

• I've tested the PDF upload and context integration with various document types by running Chatbot Arena locally