"Global State Management" Chapter - add a "struct of signals" option & example

[diversable]

Add a new option and example to the Global State Management chapter that describes passing state down using a struct of signals.

Recommended by 'gbj' on Discord:
"""
Skimming over it[the Global State Management chapter], I see the recommendations as
you do not need this chapter
Option 1 URL should drive global state
Option 2 passing signals through context or props
Option 3 global state struct and slices

Maybe 3 should be 4, and a new Option 3 should be inserted with a struct of signals
"""