cert-manager: step 7 of 7 — v1.20.3 to v1.21.1, the target (#0051)

Seven minors in sequence, each with the latest patch, exactly as the
documentation requires. Every step was verified before the next one started:
three deployments on the new version and fifteen certificates Ready.

The measured point of the exercise: v1.14.0 carried 8 critical and 128 high
findings across controller, webhook and cainjector; v1.21.1 carries 0 and 24.
The next scan round will show it in the dashboard rather than in this message.

apps/base/infra/cert-manager.yaml

@@ -15,7 +15,7 @@ spec:
       # Weg: 1.15.5 -> 1.16.5 -> 1.17.4 -> 1.18.6 -> 1.19.6 -> 1.20.3 -> 1.21.1
       # Am Zielimage gemessen: v1.14.0 traegt 8 CRITICAL und 128 HIGH ueber die
       # drei Images, v1.21.1 traegt 0 und 24.
-      version: "v1.20.3"
+      version: "v1.21.1"
       sourceRef:
         kind: HelmRepository
         name: jetstack