[Refactor] Showcase specific use case dealing with object-like variables and multi user

[FlorianJacta]

A user had an issue while developing an application (Avaiga/taipy#1378 (reply in thread)). He created different variables and modified them through multiple clients; each client shared these variables without the user knowing about it. He wanted these variables to be specific to each state. He had to assign his variables through the on_init.

The documentation doesn't really show that variables in the state can sometimes be shared when manipulating complex objects.