Move code samples to separate files and revise the whole docs

[vdusek]

• Move doc code samples to separate files to be able to perform static analysis.
  • In the same way as we did in Crawlee in docs: move code samples to separate files crawlee-python#457.
• Revise the whole documentation, update the text and fix the code samples if necessary.
  • In the same way as we did in SDK in docs: Move code samples to files and other updates apify-sdk-python#378.