What design pattern would be suitable for async image processing?

I have an app where user can select bunch of images and apply some backend async processing on them. Typical payload front frontend app looks like this:

{
 files: ['tmp.jpg', 'tmp2.jpg'],
 config: {'applyX': true, 'applyY': true},
}

Where applyX, applyY are namespaces for some processing functions. I want pattern to give ability to easily add new functions and unit test it properly.