ImageUpload component

[Rileran]

Description

An ImageUpload component would allow the user to upload an image from their storage system onto a server / provider, and display the resulting image.

This component would have its Field counterpart, integrating nicely with Formiz.

As it is hard to make such component provider agnostic, it may be a good idea to integrate it first with a known image provider (like cloudinary, and then iterate over this first version. Documentation would therefore be needed to setup said provider.

[yoannfleurydev]

Work in progress in #431