Feature/fastapi

Merge Request: OpenAI Tokenization & Model Selection

Description

This merge request implements the following two tasks:

1. Standardizing Tokenization:
   • The library tiktoken (or equivalent) is used to ensure accurate tokenization.
2. Model Selection Handling:
   • Incorporates logic for managing model selection (e.g., gpt-3.5-turbo, gpt-4).
   • create config folder for later use