When talking to an HTTP2 server, there are situations where it needs to
"rewind" the Request.Body. To allow this, we have to set up the Request.GetBody
function to return a brand new instance of the body.

If not set, we can end up with the following error:

    http2: Transport: cannot retry err [http2: Transport received Server's graceful shutdown GOAWAY] after Request.Body was written; define Request.GetBody to avoid this error

See this commit for more information: https://sourcegraph.com/github.com/golang/net/-/commit/cffdcf672aee934982473246bc7e9a8ba446aa9b?visible=2