feat(config): add Cloudflare R2 filesystem configuration

- Added new environment variables for Cloudflare R2 access key, secret access key, bucket, endpoint, and URL in the .env.example file.
- Updated composer.json to include the league/flysystem-aws-s3-v3 package.
- Modified the filesystems.php configuration file to include a new 'r2' disk for Cloudflare R2 storage.

composer.json

@@ -21,6 +21,7 @@
         "laravel/pulse": "^1.0@beta",
         "laravel/sanctum": "^3.2",
         "laravel/tinker": "^2.8",
+        "league/flysystem-aws-s3-v3": "^3.0",
         "saade/blade-iconsax": "^1.1",
         "spatie/laravel-backup": "^8.3",
         "spatie/laravel-query-builder": "^5.6",