feat: sync editor configs

[ojeytonwilliams]

• feat: sync tiptap extensions between editors
• fix: only add CodeBlock extension once

Checklist:

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

There doesn't seem to be an obvious reason why the preview and the working editor should display differently (as much as possible we want the working editor to be WYSIWYG).

This does change the preview.

Before:

After:

[Sembauke]

That I didn't think about this...