Describe the feature that you would like added

At the moment, there is no standard for our Storybook asset folders. This means that these folders are not excluded from the packaging process and we end up shipping images unnecessarily.
We should define a standard for it like, for example, an assets folder on the root of the package folder, or under each stories folder and add that to the .npmignore file.

What component or utility would this be added to

All packages

Have you discussed this feature with our team, and if so, who

@Hotell

Additional context/screenshots

Check #21695 (comment)