🐁 Provide demo-only hooks for demo switching

[asvae]

There are 2 cases we want to cover with this:

• We need a hook for comoponent setup (in majority of cases only one hook is needed, as global state will be overriden and we don't need disassembly step).
• Sometimes disassembly is still important. It might also prevent non destroyed component from erroring out.

Implementation wise

• We probably want to postpone router navigation until previous page is destroyed, that way onCreate/onDestroy would work just fine.

// Not sure if needed

• onDemoEnter - should always trigger after onDemoLeave of previously visited component.
• onDemoLeave