Fix missing prop for content editor stories

What does this MR do and why?

Adds the missing markdownDocsPath property to the content editor stories.

The required prop was introduced in !120850 (diffs)

Screenshots or screen recordings

No visual changes, just one less error message in the console 😅

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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