Docs: need to show how to use separate journal for Akka.Cluster.Sharding actors

[Aaronontheweb]

Please describe what you are trying to understand

A common pattern for making it easy to cleanup Akka.Cluster.Sharding state is to store the journal / snapshot events into separate instances for the Akka.Cluster.Sharding /system actors specifically - this has been supported for years but is not well-documented currently outside of some samples and blog posts.

Which pages have you looked at?

https://getakka.net/articles/clustering/cluster-sharding.html

What did these pages not make clear?

How to use akka.persistence.journal.sharding and akka.persistence.snapshot-store.sharding

How can we do it better?

Need to add a small section that demonstrates how to do this, what the effects are, and why you'd want to do it.