Add the ability to attach a file that is already uploaded to cloudinary to a model

[SlimGee]

This PR allows to attach a file on cloudinary by passing a public id to the attachCloudinaryMedia($publicId) method. Adds some non breaking changes

• A public Id will now be stored locally along with filename and size, useful when one wants to use the underlying cloudinary api
• Attach a file that was already uploaded to cloudinary