Generate and push multi-arch docker manifest list

Change amd64 docker image to use a `-amd64` suffix, consistent with
other architectures.  Introduce a multiarch docker manifest list with
the original (no-arch) docker tag.

Fixes #10380

scripts/build-docker

@@ -7,9 +7,9 @@ if [ "$#" -ne 1 ]; then
   exit 1
 fi
 
-VERSION=${1}
 ARCH=$(go env GOARCH)
-DOCKERFILE="Dockerfile-release"
+VERSION="${1}-${ARCH}"
+DOCKERFILE="Dockerfile-release.${ARCH}"
 
 if [ -z "${BINARYDIR}" ]; then
   RELEASE="etcd-${1}"-$(go env GOOS)-$(go env GOARCH)
@@ -23,11 +23,6 @@ if [ -z "${BINARYDIR}" ]; then
   tar -zvxf "${TARFILE}"
 fi
 
-if [ "${ARCH}" != "amd64" ]; then
-  DOCKERFILE+=".${ARCH}"
-  VERSION+="-${ARCH}"
-fi
-
 BINARYDIR=${BINARYDIR:-.}
 BUILDDIR=${BUILDDIR:-.}