chore: use note aside for notes

[gikf]

Checklist:

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

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• There were few occurrences of text marked as Note, that were not using the note aside/callout. This change makes them more prominent visually.
• src/content/docs/curriculum-file-structure.md has changes adding indentation with 3 spaces. Not sure what's up with that, but it's what prettier wanted and did when running pnpm run format.