Support for already uploaded files to "addMedia" without overwriting/deleting the existing

[Braunson]

I have media that's already been uploaded on to a disk (i.e. S3) the same disk we use for the site, the idea is to be able to "addMedia" without overwriting the existing (original) file with the same thing or delete it but instead add it to the Media table and trigger resizing responsive and custom conversions on the media.