feat(cilium): add toggle to enable or disable the Envoy proxy (#695)

Add a `cilium_envoy` variable (default true, matching upstream Cilium 1.20
which installs Envoy by default) that controls whether the Envoy proxy is
deployed for Cilium L7 policies. Pass it to Helm as `envoy.enabled` so users
with no L7 policies can skip Envoy to save resources.

- roles/k3s_server_post/defaults/main.yml: add cilium_envoy: true default
- roles/k3s_server_post/tasks/cilium.yml: add --helm-set envoy.enabled to the
  install/upgrade command, driven by the cilium_envoy conditional
- inventory/sample/group_vars/all.yml: document cilium_envoy sample var
- .github/scripts/test-cilium-envoy-toggle.py: regression test asserting the
  install command carries the envoy.enabled helm-set and renders true/false
- .pre-commit-config.yaml: wire the new test into pre-commit

Co-authored-by: Léo Nonnenmacher <leo@nonnenmacher-logel.fr>

.pre-commit-config.yaml

@@ -70,6 +70,15 @@ repos:
           - Jinja2>=3.1
         pass_filenames: false
         files: ^roles/k3s_server_post/templates/cilium\.crs\.j2$|^\.github/scripts/test-cilium-bgp-manifest\.py$
+      - id: cilium-envoy-toggle-test
+        name: Cilium Envoy toggle test
+        entry: python3 .github/scripts/test-cilium-envoy-toggle.py
+        language: python
+        additional_dependencies:
+          - Jinja2>=3.1
+          - PyYAML
+        pass_filenames: false
+        files: ^roles/k3s_server_post/tasks/cilium\.yml$|^\.github/scripts/test-cilium-envoy-toggle\.py$
       - id: kube-vip-manifest-test
         name: kube-vip manifest test
         entry: python3 .github/scripts/test-kube-vip-manifest.py