Add example for querying/filtering with puter.kv.list

[reynaldichernando]

with puter.kv, it's not really obvious how to perform querying/filtering unlike in SQL making it hard for people to add these kinds of feature

we do support it however, and thats by designing the keys and using patterns, details: https://developer.puter.com/tutorials/kv-guide/#prefix-patterns

we would like to add an example (and linked to playground) that shows how this work in detail