Fix streaming error handling to be compatible with middleware stack

[anakinj]

When streaming, HTTP errors were handled by a detached instance of Faraday::Response::RaiseError from within the on_data callback. This caused issues with custom middleware never getting a chance to see or handle these errors.

The proposed fix is to instead of raising errors manually, we build the raw body for the registered middleware to react on.

The original behavior was first introduced in #344

#591 and #635 are touching the issue a bit, but those are focusing on fixing the problem described in #479

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