Added new menu option

.devcontainer/devcontainer.json

@@ -16,5 +16,11 @@
   ],
   "preCreateCommand": "cargo build --release && cargo check",
   "postStartCommand": "./target/release/node-template --dev --ws-external",
+  "menuActions": [
+    {"id": "polkadotjs",
+     "label": "Open PolkadotJS Apps",
+     "type": "external-preview",
+     "args": ["https://polkadot.js.org/apps/?rpc=wss%3A%2F%2F/$HOST/wss"]}
+  ],
   "image": "paritytech/substrate-playground-template-node-template:latest"
 }