Add DriftIgnoreRules support to flux diff kustomization

Signed-off-by: Dipti Pai <diptipai89@outlook.com>
Assisted-by: GitHub Copilot/Claude Opus 4.7

cmd/flux/testdata/diff-kustomization/flux-kustomization-drift-ignore.yaml

@@ -0,0 +1,19 @@
+---
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: podinfo
+spec:
+  interval: 5m0s
+  path: ./kustomize
+  force: true
+  prune: true
+  sourceRef:
+    kind: GitRepository
+    name: podinfo
+  targetNamespace: default
+  ignore:
+    - paths:
+        - "/spec/ports"
+      target:
+        kind: Service