feat(commands): add GenerateSitemapCommand for sitemap generation

- Added GenerateSitemapCommand to create sitemap.xml
- Updated Kernel to schedule sitemap generation weekly
- Updated composer.json with spatie/laravel-sitemap dependency

app/Console/Kernel.php

@@ -13,6 +13,8 @@ class Kernel extends ConsoleKernel
     protected function schedule(Schedule $schedule): void
     {
         $schedule->command('db:seed --force')->twiceDaily(1, 13)->timezone('Europe/Amsterdam');
+
+        $schedule->command('sitemap:generate')->weekly();
     }
 
     /**