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.

.env.example

@@ -33,6 +33,12 @@ QUEUE_CONNECTION=sync
 SESSION_DRIVER=file
 SESSION_LIFETIME=120
 
+CLOUDFLARE_R2_ACCESS_KEY_ID=
+CLOUDFLARE_R2_SECRET_ACCESS_KEY=
+CLOUDFLARE_R2_BUCKET=
+CLOUDFLARE_R2_ENDPOINT=
+CLOUDFLARE_R2_URL=
+
 MEMCACHED_HOST=127.0.0.1
 
 REDIS_HOST=127.0.0.1