Feature/upload images background

[leihuayi]

This feature works also as a fix for the issue of swiftclient sometimes failing to upload images to OVH.
Instead of the previous workflow:

1. user uploads image to client
2. client (frontend) sends image as bytes to api (backend)
3. backend uploads bytes image to ovh swift
4. meanwhile, backend processes bytes image with ML algorithm
5. when the upload and ML analysis are finished, return result and url to location of image in swift
6. display in client (frontend) url of image in swift

Now do:

1. user uploads image to client
2. client (frontend) sends image as bytes to api (backend)
3. backend processes bytes image with ML algorithm
4. when the ML analysis are finished, return result
5. backend then uploads image to swift as a background process
6. meanwhile, the client has received the response from backend and displays image using the byte data originally uploaded by user