feat: use the Python course as a template for a new JavaScript course

[honzajavorek]

This is a proof of concept exploring whether using the Python course as a template for a brand new JavaScript course would take less time than trying to improve the original JavaScript course. This work is sanctioned by both @mnmkng and @TC-MO. If viable, this should have the potential to implement #1550 and, of course, deprecate #1579

Challenges

• Rewrite the lessons to use JS technologies, which often significantly differ.
  • replace httpx with fetch https://nodejs.org/en/learn/getting-started/fetch & https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
  • replace bs4 with cheerio https://cheerio.js.org/ because https://crawlee.dev/js/api/cheerio-crawler/class/CheerioCrawler
  • use https://github.com/juanjoDiaz/json2csv, the original package is abandoned
• See if the original JS course contains stuff which isn't in the Python course, but we want to keep it in some form.
  • lesson about Headless browsers - we could add it to both Python and JS course (after crawlee lesson?)
• Make sure we're not duplicating images etc.
• Make sure all historical links lead somewhere.

Todo

• don't forget any /TBD/ occurrences
• resolve the temporary symlink to the images directory
• eventually rename javascript2 to javascript
• DRY intro of the course? DRY partials?
• fix sidebar position of the intro
• add redirects