cli: wrap minified code in iife

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/neat-icons-fry.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Tweaked frontend bundling configuration to avoid leaking declarations into global scope.

packages/cli/src/lib/bundler/optimization.ts

@@ -29,6 +29,7 @@ export const optimization = (
     minimizer: [
       new ESBuildMinifyPlugin({
         target: 'es2019',
+        format: 'iife',
       }),
     ],
     runtimeChunk: 'single',