Fix Colab compatibility: Add directory setup

[aksh7j]

This code detects if the notebook is running in Google Colab and sets up the required directory structure for the housing dataset.

[ageron]

Thanks for the PR, @aksh7j , but I don't understand why this is needed? The notebook downloads whatever data is needed and already creates the directories:

Path("datasets").mkdir(parents=True, exist_ok=True)  # creates the datasets directory if needed

and:

housing_tarball.extractall(path="datasets")  # extract the tarball which creates the subdirectory

Did you run into any error?