net/http: upon http redirect, copy Request.GetBody in new request
This enable http.RoundTripper implementation to retry POST request (let's
say after a 500) after a 307/308 redirect.
Fixes #73439
Change-Id: I4365ff58b012c7f0d60e0317a08c98b1d48f657e
Reviewed-on: https://go-review.googlesource.com/c/go/+/666735 Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Damien Neil <dneil@google.com>