feat: Add DB Connector API & Secure Configuration

[Mario928]

Summary

This PR introduces a standalone module for extracting student conversation data from the Open WebUI database.

Key Changes

New db_connector Module

• Adds a FastAPI service to extract and aggregate chat data
• Supports filtering by Group, Model, and Date
• Saves outputs as structured JSON files locally

Security Enhancements

• Removed hardcoded API keys from utils.py
• Added .env support (via python-dotenv) for DATABASE_URL and PORTKEY_API_KEY
• Added .gitignore to prevent accidental secret commits

Documentation

• Updated README.md with detailed Security and Database Connector deployment instructions
• Added todo.md tracking the connector implementation status
• Consolidated dependencies into a root requirements.txt

Verification

• Tested the connector API and verified that data is received and stored properly (see todo.md in db_connector for more details)