Docs modifications (#5804)

- Fixes #5504
- Fixes #5503
- Return 404 when the page does not exist
- Modified the footer in order to align it properly
- Removed "noticed something to change" in each table of content
- Fixed the URLs of the edit module 
- Added the edit module to Developers
- Fixed header style on the REST API page.
- Edited the README to point to Developers
- Fixed selected state when clicking on sidebar elements

---------

Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-website/src/app/twenty-ui/[slug]/page.tsx

@@ -1,4 +1,5 @@
 import { Metadata } from 'next';
+import { notFound } from 'next/navigation';
 
 import DocsContent from '@/app/_components/docs/DocsContent';
 import { fetchArticleFromSlug } from '@/shared-utils/fetchArticleFromSlug';
@@ -27,5 +28,8 @@ export default async function TwentyUISlug({
 }) {
   const basePath = '/src/content/twenty-ui';
   const mainPost = await fetchArticleFromSlug(params.slug, basePath);
+  if (!mainPost) {
+    notFound();
+  }
   return mainPost && <DocsContent item={mainPost} />;
 }