DetailedApiRequestError.toString() should print more information

I've often found the `DetailedApiRequestError.jsonResponse` to contain critically important information about errors...

Maybe we could just dump that as part of the error messages using `toString()`, if we pretty print it with indentation it probably doesn't matter so much if it's a huge blob.

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I'm not entirely sure if any APIs would include sensitive information in error messages that you wouldn't want to risk leaking into logs. But I suspect that's not the case, although it can never be excluded as users could be doing anything..