add .gitignore to Enhance Project Cleanliness and Security

[pChitral]

Objective:
This pull request introduces a .gitignore file to the ISLP_labs repository to prevent the inclusion of unnecessary or sensitive files that can clutter the project and compromise security.

Benefits:

• Clean Repository: Helps in maintaining a clean project space by excluding temporary and compiled files like __pycache__, .ipynb_checkpoints, and environment directories (venv/, env/).
• Enhanced Security: Reduces the risk of accidentally committing sensitive configuration details from local development environments.

Included in .gitignore:

• Temporary files such as Python bytecodes and Jupyter Notebook checkpoints.
• Environment and configuration files for IDEs like VSCode and PyCharm.
• System-generated files like .DS_Store and build directories.

Conclusion:
Adding this .gitignore helps align the repository with best practices for Python projects, ensuring a cleaner and more secure collaboration environment.

[tschm]

@jonathan-taylor Please merge this. The .python-version should not be ignored though. Also you may want to ignore .venv which is a standard