Support ESM for the styleguide.config.js file

[a-maggi]

The problem

The upcoming version of react-docgen will no longer support the require statement, as it is now completely written as an ESM (ECMAScript Modules) package. We need support to use ESM import for the styleguide.config.js file in order to accommodate use cases like this.

Additional context

We have already attempted to rename the file to the cjs extension, but it did not resolve the issue.