make public storage and direct upload optional

app/controllers/api/attachments_controller.rb

@@ -7,7 +7,14 @@ module Api
     def create
       submitter = Submitter.find_by!(slug: params[:submitter_slug])
 
-      blob = ActiveStorage::Blob.find_signed(params[:blob_signed_id])
+      blob =
+        if (file = params[:file])
+          ActiveStorage::Blob.create_and_upload!(io: file.open,
+                                                 filename: file.original_filename,
+                                                 content_type: file.content_type)
+        else
+          ActiveStorage::Blob.find_signed(params[:blob_signed_id])
+        end
 
       attachment = ActiveStorage::Attachment.create!(
         blob:,