Support the specific OpenRefine/SDC upload workflow from a IIIF endpoint

When talking to potential users of the Structured Data on Commons (SDC) batch upload functionalities for OpenRefine, we hear a lot about the use case of IIIF endpoints.

IIIF is the International Image Interoperability Framework. According to the framework's website it is "a set of open standards for delivering high-quality, attributed digital objects online at scale. It’s also an international community developing and implementing the IIIF APIs. IIIF is backed by a consortium of leading cultural institutions."

Many cultural institutions around the world present their files through a IIIF endpoint. This is indeed a section-wide API standard.

Many IIIF endpoint managers are, or may be, interested to upload files to Wikimedia Commons leveraging this specific set of APIs.

1. In any endpoint, the source files to be uploaded to Wikimedia Commons can be called upon in a specific standardized way.
2. Metadata about the files (if present) can also be called upon in the same kind of standardized way.

OpenRefine users can use both of these specific API calls, during project creation and while wrangling data inside OpenRefine. But that's advanced stuff, and we can make that process easier.

We can tackle this in various ways:

1. Lightweight, documentation-focused approach: we don't build specific features for IIIF users but we document the process well for them;
2. And/or (perhaps at a later stage, if we see a lot of interest in this) we indeed create a specific IIIF-focused feature or wizard, probably to be used during project creation.

Start by reviewing the IIIF endpoint API calls described in the issue and the existing OpenRefine project-creation and data-wrangling workflow. Decide whether the first deliverable is documentation or a IIIF-focused feature, then define completion as either a documented end-to-end upload process or an agreed wizard scope.