Copy-pasting code snippets in scenario tutorial does not work

[AlexandreSajus]

This feedback comes from a one-hour beta testing session of scenario management.

In this tutorial: https://docs.taipy.io/en/develop/knowledge_base/tutorials/scenario_management_overview/

Copy-pasting each code snippet will generate non-functional code (the data was never loaded) which is unintuitive. We should add the missing code snippets so that the user does not have to go to the bottom of the page to copy-paste the entire code for the tutorial to work