Transform copying static assets

[apobbati]

Need to have an ability to transform the assets specified in the copy object. For example, I have a set of images that I'd like to be able to optimize based on file extension, file path, etc. Currently, there's no way to do it.

[chmontgomery]

👍 love the idea! If you have time I'd accept a PR

[timelf123]

This would be amazing for imagemin on copied images