fix: refactor command syntax for Docker registry configuration

nodes/heimdall/docker_registry/compose.yaml

@@ -12,8 +12,13 @@ services:
       # We pass the raw hash string here
       - HT_CONTENTS=${REGISTRY_AUTH_HTPASSWD_CONTENTS}
     # Create the file on the fly before the registry starts
-    command: >
-      sh -c "mkdir -p /auth && echo '$$HT_CONTENTS' > /auth/htpasswd && exec bin/registry serve /etc/docker/registry/config.yml"
+    command: 
+      - sh
+      - -c
+      - |
+        mkdir -p /auth
+        echo "${HT_CONTENTS}" > /auth/htpasswd
+        exec bin/registry serve /etc/docker/registry/config.yml
     volumes:
       - /mnt/appdata/docker_registry/data:/var/lib/registry
     networks: