fix(dashboard): add VITE_LEGACY_DASHBOARD_URL to environment script (#8572)

Author: merrcury

apps/dashboard/docker-entrypoint.sh

@@ -4,7 +4,8 @@
 ENV_SCRIPT="<script>
   window._env_ = {
     VITE_API_HOSTNAME: '${VITE_API_HOSTNAME}',
-    VITE_WEBSOCKET_HOSTNAME: '${VITE_WEBSOCKET_HOSTNAME}'
+    VITE_WEBSOCKET_HOSTNAME: '${VITE_WEBSOCKET_HOSTNAME}',
+    VITE_LEGACY_DASHBOARD_URL: '${VITE_LEGACY_DASHBOARD_URL}'
   };
 </script>"