Add VS Code remote extensions

Author: josephbwagner

.devcontainer/devcontainer.json

@@ -15,7 +15,11 @@
 	},
 
 	// Add the IDs of extensions you want installed when the container is created.
-	"extensions": []
+	"extensions": [
+    "ms-azuretools.vscode-docker",
+    "scalameta.metals",
+    "oderwat.indent-rainbow"
+  ]
 
 	// Use 'forwardPorts' to make a list of ports inside the container available locally.
 	// "forwardPorts": [],