Add File Search Functionality to OpenAI Discord Bot

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This pull request introduces new file search capabilities to the OpenAI Discord Bot, enhancing its ability to fetch and utilize file-based resources via OpenAI's API. This update allows the bot to handle file search operations, making it more versatile in processing user queries that require context from external files.

Changes Made

1. File Search Integration: Implemented the ability to use the file_search tool within OpenAI API calls. This is configured to pull file data using vector store IDs which can be set via environment variables for better security and flexibility.
2. Environment Variable Setup: Added a new environment variable VECTOR_STORE_ID to manage the vector store IDs securely outside of the codebase.

How to Use

To utilize the file search functionality:

1. Set the VECTOR_STORE_ID in your .env file.
2. Ensure your OpenAI API key has permissions to access file search capabilities.
3. Use commands designed to trigger file search operations as documented in the updated README.