DEV: allow using CDN URL for all s3 uploads (#20755)

This adds an option to allow non-image s3 files to be downloaded through CDN URL.

Addresses the issues in:

* meta.discourse.org/t/s3-cdn-url-not-being-used-on-non-image-uploads/175332
* meta.discourse.org/t/s3-uploads-using-cdn-for-pdfs/213218

spec/lib/upload_creator_spec.rb

@@ -375,6 +375,18 @@ RSpec.describe UploadCreator do
         expect(stored_upload.url).not_to eq(signed_url)
         expect(signed_url).to match(/Amz-Credential/)
       end
+
+      it "should return CDN URL when enabled" do
+        SiteSetting.s3_use_cdn_url_for_all_uploads = true
+        SiteSetting.authorized_extensions = "pdf"
+        SiteSetting.s3_cdn_url = "https://example-cdn.com"
+
+        upload = UploadCreator.new(pdf_file, pdf_filename, opts).create_for(user.id)
+        stored_upload = Upload.last
+        cdn_url = Discourse.store.url_for(stored_upload)
+
+        expect(cdn_url).to match(/example-cdn\.com/)
+      end
     end
 
     context "when the upload already exists based on the sha1" do