Make buildkite push images with gcr.io at release pipeline.

GCR will be deprecated, while the prefix `gcr.io` will be
be hosted via Artifact Registry. By adding this one extra step,
all test images will be accessible via both `gcr.io` and
`pkg.dev`.

PiperOrigin-RevId: 694278137

Author: milantracy

.buildkite/release.yaml

@@ -24,13 +24,15 @@ steps:
     if: build.branch == "master" && build.tag == null
     commands:
       - make ARCH=x86_64 DOCKER_PUSH_AS_LATEST=true push-all-images
+      - make ARCH=x86_64 REMOTE_IMAGE_PREFIX=gcr.io/gvisor-presubmit DOCKER_PUSH_AS_LATEST=true push-all-images
     agents:
       arch: "amd64"
   - <<: *common
     label: ":ship: Push all images (aarch64)"
     if: build.branch == "master" && build.tag == null
     commands:
       - make ARCH=aarch64 DOCKER_PUSH_AS_LATEST=true push-all-images
+      - make ARCH=aarch64 REMOTE_IMAGE_PREFIX=gcr.io/gvisor-presubmit DOCKER_PUSH_AS_LATEST=true push-all-images
     agents:
       arch: "arm64"
   - <<: *common

images/README.md

@@ -52,9 +52,8 @@ if available.
 ## Building and pushing images
 
 All images can be built manually by running `build-<image>` and pushed using
-`push-<image>`. Note that you can also use `build-all-images` and
-`push-all-images`. Note that pushing will require appropriate permissions in the
-project.
+`push-<image>`. Note that you can also use `push-all-images`. Note that pushing
+will require appropriate permissions in the project.
 
 The continuous integration system can either take fine-grained dependencies on
 individual `push` targets, or ensure all images are up-to-date with a single