Add E2E test infrastructure for kube-vip plugin

Scaffolded via e2e-scaffold.sh (proactive improvement).
- playwright.config.ts, e2e/auth.setup.ts, e2e/kube-vip.spec.ts
- scripts/deploy-e2e-headlamp.sh, scripts/teardown-e2e-headlamp.sh
- .github/workflows/e2e.yaml uses reusable workflow
- @playwright/test ^1.58.2 devDep

- PRI-641

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitignore

@@ -5,3 +5,9 @@ dist/
 .env
 .env.local
 .eslintcache
+
+# E2E
+e2e/.auth/
+.env.e2e
+playwright-report/
+test-results/