Add prettier as recommended extension to workspace

.vscode/extensions.json

@@ -0,0 +1,9 @@
+{
+    // See https://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
+    // Extension identifier format: ${publisher}.${name}. Example: vscode.csharp
+
+    // List of extensions which should be recommended for users of this workspace.
+    "recommendations": ["esbenp.prettier-vscode"],
+    // List of extensions recommended by VS Code that should not be recommended for users of this workspace.
+    "unwantedRecommendations": []
+}