Add python decouple to the application

# Description

Python Decouple strictly separates the settings parameters from the source code. It adds parameters related to an instance of the project into a seperate .env file. All the environment-specific parameters (secret key, user, passwords, debug status and hosts to mention a few) can be kept into and changed from a single configuration module. Also, It enables changing parameters without having to redeploy the app.

Adding this into .gitignore ensures these are not pushed with the code.

Look for the Django settings file (likely settings.py) to see how configuration is currently managed. Install python-decouple, create a .env file for environment variables, and update settings.py to use config() from decouple. Ensure .env is added to .gitignore. Test that the application runs with the new configuration setup.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.