S3 Set base URL for uploaded image URL

[WakuwakuP]

trafficstars

You may want to set a URL separate from the API URL, for example if you want to access images via a CDN.

Example: To use Cloudflare R2, you need to set a custom domain for public access separate from the API.

API URL: https://<id>.r2.cloudflarestorage.com/<bucket_name> Public URL: https://<custom_domain>/<object_key>