Merge pull request #39406 from vipulnsward/ar-bookstore-model

Changes over AR Querying guide making use of Bookstore example

guides/CHANGELOG.md

+*   Use Bookstore as a unified use-case for all examples in Active Record Query Interface Guide.
+
+    *Ashley Engelund*, *Vipul A M*
 
 
 Please check [6-0-stable](https://github.com/rails/rails/blob/6-0-stable/guides/CHANGELOG.md) for previous changes.