[Prioritized] Feature req: option to not serialize/deserialize request body

As I mentioned in the sync yesterday:

Some methods for ACR require validation of the response body against a `Docker-Content-Digest` header. The test proxy serializes the response body during recording mode and deserializes it during playback, which causes any whitespace in the response body to be discarded. This means that the recomputed digest is different to what is in the Docker-Content-Digest header, causing tests to pass in live/record mode but fail in playback mode.

An option where the test proxy does not serialize the response body (so it just records it byte-for-byte, regardless of the content type) would be fantastic.