ci-automation/release.sh: use rclone docker image

rclone was previously called from the Mantle image but it's not the
 case anymore because we need some environment variables (CHANNEL, ARCH,
 etc.)

 Let's switch to the `rclone` Docker image.

Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>

ci-automation/release.sh

@@ -167,9 +167,12 @@ function copy_from_bincache_to_bucket() {
     echo "Experimental (i.e ignore if it fails) - copy the images to CloudFlare bucket"
     (
     set +eu
-    rclone --config "${RCLONE_CONFIGURATION_FILE}" \
-      sync \
-      --http-url "https://${BUILDCACHE_SERVER}/images/${arch}/${version}" :http: "r2:flatcar/${channel}/${arch}-usr/${version}"
+    docker run --rm -ti \
+      -v "${RCLONE_CONFIGURATION_FILE}:/opt/rclone.conf:ro" \
+      docker.io/rclone/rclone:1.71.1 \
+        --config "/opt/rclone.conf" \
+        sync \
+        --http-url "https://${BUILDCACHE_SERVER}/images/${arch}/${version}" :http: "r2:flatcar/${channel}/${arch}-usr/${version}"
     # Exit the function cleanly for now:
     true
     )