feat: lessons about crawling and scraping product detail pages in Python

[honzajavorek]

Done

This PR introduces two new lessons to the Python course, including real-world exercises. These two lessons conclude the base of the course, as at the end of the course the reader should be able to build their own scraper. The final exercises focus on that fact and test the reader's ability of independent building. The PR also includes some edits to the previous parts of the course (code examples, exercises).

Next

Before the course is done, there should be two more lessons: One about building the very same scraper using a framework (Crawlee), and one about deploying the scraper to a platform (Apify). Then I should return back to the beginning and complete the three initial lessons about DevTools.