webui: Tweak prettier setup

This should make us more consistent on formatting in local vs CI
diff --git a/.vscode/extensions.json b/.vscode/extensions.json
new file mode 100644
index 0000000..ebf4c17
--- /dev/null
+++ b/.vscode/extensions.json
@@ -0,0 +1,5 @@
+{
+  // See http://go.microsoft.com/fwlink/?LinkId=827846
+  // for the documentation about the extensions.json format
+  "recommendations": ["esbenp.prettier-vscode"]
+}