Place files in separate folders

[IanVS]

I'm proposing to add unbuild to a storybook package, but their convention is to place the outputs into different folders, like:

dist/cjs/index.js
dist/esm/index.js

And actually, what I want is:

dist/cjs/index.cjs
dist/esm/index.mjs

Is that possible? I can't tell from looking at the names of the options.