Add E2E test infrastructure for argocd plugin

- playwright.config.ts with authenticated test projects
- e2e/auth.setup.ts authenticates via OIDC or token
- e2e/argocd.spec.ts smoke tests for sidebar, applications list,
  and plugin settings
- scripts/deploy-e2e-headlamp.sh deploys Headlamp + argocd in headlamp-dev
- scripts/teardown-e2e-headlamp.sh cleans up after tests
- e2e.yaml uses reusable workflow from .github repo
- @playwright/test ^1.58.2 devDep added

- PRI-638

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

.github/workflows/e2e.yaml

@@ -0,0 +1,23 @@
+name: E2E Tests
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: e2e-${{ github.repository }}
+  cancel-in-progress: false
+
+jobs:
+  e2e:
+    uses: privilegedescalation/.github/.github/workflows/plugin-e2e.yaml@main
+    with:
+      node-version: '22'
+      headlamp-version: v0.40.1
+      e2e-namespace: headlamp-dev