Add FastAPI + MongoDB sample app

[Yuvraajb]

This pull request introduces a new sample application to the Keploy Python Samples repository: FastAPI + MongoDB. The app demonstrates a modern, async CRUD API for student management, built with FastAPI and Motor (async MongoDB driver).

Motivation

While the repo already features samples for Flask+Mongo, Django+Postgres, FastAPI+Postgres, and others, there was no example for the increasingly popular FastAPI + MongoDB stack. This addition fills that gap, providing the community with a real-world, production-style template for building and testing async APIs with Keploy.

What’s Included
• ‎⁠fastapi-mongo/⁠ directory with:
▫ ‎⁠main.py⁠: Async FastAPI CRUD API for students
▫ ‎⁠requirements.txt⁠: All necessary dependencies
▫ ‎⁠Dockerfile⁠: For easy containerization
▫ ‎⁠README.md⁠: Clear setup and usage instructions

How to Use

1. Install dependencies with ‎⁠pip install -r requirements.txt⁠
2. Start MongoDB (locally or via Docker)
3. Run the app using ‎⁠uvicorn main:app --reload⁠
4. Explore and test the API at ‎⁠/docs⁠