webpack5: add Buffer plugin

Signed-off-by: Tim Hansen <timbonicus@gmail.com>

.changeset/ninety-ducks-relate.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Add Buffer to `ProvidePlugin` since this is no longer provided in `webpack@5`

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

@@ -119,6 +119,7 @@ export async function createConfig(
   plugins.push(
     new ProvidePlugin({
       process: 'process/browser',
+      Buffer: ['buffer', 'Buffer'],
     }),
   );