Helper to upload an image to an URL

This new helper, in arkindex_worker.image will implement the upload of a Pillow Image to an URL. We need some retry mechanism on the PUT call, similar to _retried_request. We could generalize that function to support both GET and PUT calls, or write a second helper with the same retry mechanism.

b = BytesIO()
pil_image.save(b, format="jpeg")
b.seek(0)
resp = requests.put(url, data=b)
resp.raise_for_status()
return resp