createSignedUrls should allow for storage transformations per image in the same was createSignedUrl does

[kkukshtel]

As the title say — the options available for createSignedUrls differs from that of createSignedUrl. If I want signed URLs of transformed images (I do), I need to call createSignedUrl for each image in a loop instead of being able to issue a single API call. I would think here that the transformation wouldn't be any array necessarily, and would instead apply to everything requested.