A template for an eventgrid subscription on a builtin topic would be useful

Right now there is only a template for a self created topic, but not for builtins like storage accounts. Can't figure out how to write one, get errors all the time.

Start by comparing the existing template for a self-created Event Grid topic with the requested built-in-topic scenario, especially storage accounts. Consult the repository's existing Event Grid templates and Azure guidance to identify the required subscription structure. Done means adding a working quickstart template for an Event Grid subscription on a built-in topic.

Written by the indexing model from the issue text.