Provide more info about the author from the API

[marekbrze]

Current state:
Currently there is only possibility to get creditLine and source.url from the sanity.mageAsset object if you want to give attribution to the author of the photo. creditLine doesn't follow the format proposed by Unsplash -> Photo by Andres Molina** on Unsplash. It says [user] by Unsplash. Also it's not language agnostic.

Proposed state
Add following fields from the Unsplash API to the sanity.imageAsset:

• user.name <- full user name
• user.username <- username if you want to display it as @johnsmith
• user.links.html <- link to the profile

This will provide many possibilities to display attribution information on the frontend.