Currently, we can create and store metadata for published feature layers in a map's properties. When we share the layer with Portal, all of that metadata gets copied into the metadata for the service and the item page gets that information automatically, However, there is no way to upload or reference a custom thumbnail in the map's metadata, so every time we have to overwrite a layer in Portal, we also have to go to the item page and re-upload the custom thumbnail. I would like to have a way to either store or reference the thumbnail within the Pro project and have it auto-upload when a service publishes.
