Standardize base url for uploads
We don't seem to have a standard way to retrieve the base url for uploads and it turns out we support multiple conflicting ways to set a base url via Pleroma.Upload, :base_url
and Pleroma.Uploaders.S3, :public_endpoint
.
I think completely removing Pleroma.Uploaders.S3, :public_endpoint
should be done in a separate MR.