cert-manager: scrape metrics (follow-up to #239) (#241)

Follow-up to #239. Adds a `VMServiceScrape` for cert-manager's existing webhook (`metrics` :9402) and cainjector (`http-metrics` :9402) services so the observability VMAgent collects them. No chart change needed. (The controller's own metrics need `prometheus.enabled` in the chart to expose a metrics service — separate follow-up.)

Reviewed-on: #241
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

apps/base/cert-manager/kustomization.yaml

@@ -7,3 +7,4 @@ resources:
   - serviceaccount.yaml
   - clusterrole.yaml
   - clusterrolebinding.yaml
+  - vmservicescrape.yaml

apps/base/cert-manager/vmservicescrape.yaml

@@ -0,0 +1,17 @@
+---
+# Scrape cert-manager webhook + cainjector metrics endpoints.
+# Picked up by the observability VMAgent (selectAllByDefault).
+apiVersion: operator.victoriametrics.com/v1beta1
+kind: VMServiceScrape
+metadata:
+  name: cert-manager
+  namespace: cert-manager
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/instance: cert-manager
+  endpoints:
+    - port: metrics
+      path: /metrics
+    - port: http-metrics
+      path: /metrics