This allows servers to rotate their ECH keys without needing to restart
the server.
Fixes #71920
Change-Id: I55591ab3303d5fde639038541c50edcf1fafc9aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/670655
TryBot-Bypass: Roland Shoemaker <roland@golang.org> Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Roland Shoemaker <roland@golang.org> Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>