Use Crawlee router in the framework lesson of the JS course

[honzajavorek]

The sources/academy/webscraping/scraping_basics_javascript/12_framework.md lesson could use router https://crawlee.dev/js/api/core/class/Router so that the code is better structured and the code blocks more readable. The Python version of the lesson already does that from the very beginning of the lesson.

Once we use it in the lesson, we should use it in the exercises as well, see suggestion from @B4nan here for a ready code #2097 (comment)