Hm, I don’t really understand your question. Where would you expect this data-src link to be visible in the Panel? Or do you want to add a meta data field that you can fill in in the Panel? Like a caption field etc.?
That’s not possible, the data attribute is not an intrinsic property of an image. And if you don’t want it as meta data field either, you can’t have it.
The only way to adding additional fields that are editable is via a meta data field.
You can create a custom tag, but that doesn’t help you with displaying the data attribute in the file view. With your extended version of the image tag, you can add a data attribute to images you add in a textarea field.