docs: improved SEO of documentation (#3117)

* docs: added description to documentation pages

* docs: added more descriptions

* docs: finished improving meta description

* docs: added searchbox structured data

* docs: added breadcrumbs structured data

* docs: added how to structured data

* docs: improved 404 page

* docs: added how-to frontmatter option

www/docs/src/theme/TOCItems/index.js

@@ -0,0 +1,15 @@
+import React from 'react';
+import TOCItems from '@theme-original/TOCItems';
+import StructuredDataHowTo from '../StructuredData/HowTo';
+import { useDoc } from '@docusaurus/theme-common/internal'
+
+export default function TOCItemsWrapper(props) {
+  const { frontMatter, contentTitle } = useDoc()
+  
+  return (
+    <>
+      <TOCItems {...props} />
+      {frontMatter?.addHowToData && <StructuredDataHowTo toc={props.toc} title={contentTitle} />}
+    </>
+  );
+}