Use Docker Build Cloud for releases

With QEMU the ARM64 builds are slow and not reliable. If we use the
Docker Cloud builders we reduce the build times considerably.
As a Docker OSS organisation we get 400 build minutes per month, which
should be fine, because we already use checks if builds are really
needed. The Docker Cloud also uses a cache that should reduce build
times a little bit more.

build.sh

@@ -103,6 +103,8 @@ GH_ACTION   If defined, special 'echo' statements are enabled that set the
             - FINAL_DOCKER_TAG: The final value of the DOCKER_TAG env variable
             ${_GREEN}Default:${_CLEAR} undefined
 
+CHECK_ONLY  Only checks if the build is needed and sets the GH Action output.
+
 ${_BOLD}Examples:${_CLEAR}
 
 ${0} master
@@ -355,6 +357,11 @@ else
 fi
 gh_echo "::endgroup::"
 
+if [ "${CHECK_ONLY}" = "true" ]; then
+  echo "Only check if build needed was requested. Exiting"
+  exit 0
+fi
+
 ###
 # Build the image
 ###