chore: update `getting-started/react-essentials` path (#72250)
## Description
At #51579, react-essentials.mdx was deleted.
Some URLs doesn't navigate right pages due to this change.
Then I update to correct path.
- Fixes https://github.com/vercel/next.js/issues/72566
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Co-authored-by: Sam Ko <sam@vercel.com>
