fix: correct quoting in command for Docker registry configuration

nodes/heimdall/docker_registry/compose.yaml

@@ -17,9 +17,8 @@ services:
       - -c
       - |
         mkdir -p /auth
-        echo "${HT_CONTENTS}" > /auth/htpasswd
+        echo '${HT_CONTENTS}' > /auth/htpasswd
         exec bin/registry serve /etc/docker/registry/config.yml
-    volumes:
       - /mnt/appdata/docker_registry/data:/var/lib/registry
     networks:
       - proxy-net