Upgrade Python version to 3.12 in Docker configuration

[gafda]

This pull request updates the Dockerfiles to use Python 3.12, upgrades pip usage, removes manual NLTK data downloading, and updates several dependencies to their latest versions for both runtime and testing environments. It also includes a minor docstring correction.

Dependency and environment upgrades:

• Updated base images in both Dockerfile and Dockerfile.lite from python:3.10 to python:3.12 to ensure compatibility with the latest Python features and security patches. [1] [2]
• Upgraded pip before installing requirements and removed manual NLTK data downloading and related environment variable setup, streamlining the Docker build process. [1] [2]
• Updated multiple dependencies in requirements.lite.txt to newer versions, including langchain, sqlalchemy, fastapi, unstructured, and others for improved stability, features, and security.
• Updated testing dependencies in test_requirements.txt to newer versions, such as pytest and httpx, to maintain compatibility with the latest testing tools.

Minor code cleanup:

• Fixed a minor typo in a docstring in app/utils/document_loader.py.

[danny-avila]

removes manual NLTK data downloading,

This is required, the motivation to remove was not clear