ci: add generated-changes-diff check

Fails a PR (including drafts) when it changes code that should have
triggered make manifests/generate/fmt but the regenerated output was
not committed. Modeled on kaapi's generated-changes-diff workflow,
re-scoped to byoh's own Makefile targets (no helm/airgap/kamaji
equivalents exist here).

Known issue: controller-gen v0.14.0 fails to build under Go 1.26.2 on
a fresh checkout (golang.org/x/tools@v0.16.1's tokeninternal package
no longer compiles against token.FileSet's current internal layout),
so this check will fail on every PR until that's fixed separately.

Author: indradhanush

.github/workflows/generated-changes-diff.yml

@@ -0,0 +1,27 @@
+name: generated-changes-diff
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+  push:
+    branches:
+      - main
+
+jobs:
+  run:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Install Go 1.26.2
+        uses: actions/setup-go@v6
+        with:
+          go-version: 1.26.2
+
+      - name: Check that manifests and generated code have been committed
+        run: |
+          make manifests generate fmt
+          git diff --exit-code && [ -z "$(git ls-files --others --exclude-standard)" ] || (echo "Generated files are out of date. Run 'make manifests generate fmt' locally and commit the result (including any newly generated files)." && exit 1)