[website] Fix 40x links

[mnajdova]

Fixing some dead links reported by moz.com

---

The ones left are related to the API pages of the DataGrid. Looks like the URLs for the API pages changed. The SideBar references URLs starting with /api-docs/data-grid/*, but the valid links are actually starting with /api/data-grid/*. We should either change the _redirecs:

diff --git a/docs/public/_redirects b/docs/public/_redirects
index 9678655950..65243167a0 100644
--- a/docs/public/_redirects
+++ b/docs/public/_redirects
@@ -184,7 +184,7 @@ https://v4.material-ui.com/* https://v4.mui.com/:splat 301!
 ## material-ui-x
 ## Unlike the store that expect to be hosted under a subfolder,
 ## material-ui-x is configured to be hosted at the root.
-/api/*/ https://docs-v5--material-ui-x.netlify.app/api/:splat/ 200
+/api-docs/*/ https://docs-v5--material-ui-x.netlify.app/api/:splat/ 200
 /:lang/api/*/ https://docs-v5--material-ui-x.netlify.app/:lang/api/:splat/ 200
 /components/* https://docs-v5--material-ui-x.netlify.app/components/:splat 200
 /:lang/components/* https://docs-v5--material-ui-x.netlify.app/:lang/components/:splat 200

Or fix the links in the Sidebar. Probably @m4theushw can give us more details.

Edit: this is being handled in #28176

[mui-pr-bot]

No bundle size changes

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