Introduce container_registry for image prefix

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Change-Id: I80067f53aa2b63286b654fff782f0f7b65a2d050
diff --git a/images/nova-ssh/Dockerfile b/images/nova-ssh/Dockerfile
index 45035a0..5e0e342 100644
--- a/images/nova-ssh/Dockerfile
+++ b/images/nova-ssh/Dockerfile
@@ -1,9 +1,10 @@
 # SPDX-License-Identifier: Apache-2.0
 # Atmosphere-Rebuild-Time: 2024-06-28T12:14:26Z
 
+ARG REGISTRY
 ARG RELEASE
 
-FROM harbor.atmosphere.dev/library/openstack-runtime:${RELEASE}
+FROM ${REGISTRY}/openstack-runtime:${RELEASE}
 RUN <<EOF bash -xe
 apt-get update -qq
 apt-get install -qq -y --no-install-recommends \