Merge new doc under next 14 in 5.x branch (#1977)

* Upgrade eslint and ignore no-constructor-return rule for actual constructors (#1974)

* Upgrade eslint and ignore no-constructor-return rule for actual constructors

* ignore eslint-next for now

* upgrate documentation website to next 14 (#1975)

* upgrate to next 12

* next 13

* migrate links

* next 14

* deactivate eslint for documentation once again

* Fix title warning. See vercel/next.js#38256

* start migrating to nextjs app router (#1976)

* upgrade next sitemap (#1978)

.gitignore

@@ -10,7 +10,7 @@ yarn-error.log
 TODO
 /website/.next
 /website/out
-/website/public/sitemap.xml
+/website/public/sitemap*.xml
 /website/public/robots.txt
 /gh-pages
 /npm