feat: add robots.txt and sitemap lastmod metadata for documentation site (#5156)

Author: Hjaf

apps/design-system-docs/docusaurus.config.ts

@@ -58,6 +58,9 @@ const config: Config = {
             // Add additional CSS files here
           ],
         },
+        sitemap: {
+          lastmod: 'datetime',
+        },
       } satisfies Preset.Options,
     ],
   ],

apps/design-system-docs/static/robots.txt

@@ -0,0 +1,2 @@
+User-agent: *
+Allow: /