[DNM] [Storybook] Re-enable storysource addon

[slax57]

Problem

Storybook storysource addon (allowing to display the source code for a story in the 'Code' panel) was broken since we updated to Storybook v8.

It would be nice to re-enable it to allow viewers of our storybook to also view the matching source code.

Solution

I actually managed to track down a bug in Storybook, preventing this addon to work in the first place.

This PR re-enables the plugin, and is to be merged when the issue is fixed in a new storybook release.

Blocked: wait until storybookjs/storybook#29669 is merged and released

How To Test

Run storybook, and check the source code of each story is present in the 'Code' panel.

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.