Image URLs are broken when Markdown versions of published docs #4593

Bug description

Fetching a Markdown version of a published page like this one:

https://gitbook.com/docs/create-content/blocks/insert-images.md

returns embedded images like this

<img src="/files/WNXq6RcD2e4WTRcZEz4f" alt="">

These /files/ URLs are however invalid and are not serving the desired image.

How to reproduce

1. Fetch a page in Markdown format
2. Fetch embedded images
3. Get a 404

Additional context