Update cert-manager to v1.21.0 (main) (#10398)

Update cert-manager to v1.21.0

| datasource | package                                  | from    | to      |
| ---------- | ---------------------------------------- | ------- | ------- |
| docker     | quay.io/jetstack/cert-manager-cainjector | v1.20.3 | v1.21.0 |
| docker     | quay.io/jetstack/cert-manager-controller | v1.20.3 | v1.21.0 |
| docker     | quay.io/jetstack/cert-manager-webhook    | v1.20.3 | v1.21.0 |

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

tests/data/virtual-server-certmanager/certmanager.yaml

@@ -13335,7 +13335,7 @@ spec:
           type: RuntimeDefault
       containers:
         - name: cert-manager-cainjector
-          image: "quay.io/jetstack/cert-manager-cainjector:v1.20.3"
+          image: "quay.io/jetstack/cert-manager-cainjector:v1.21.0"
           imagePullPolicy: IfNotPresent
           args:
           - --v=2
@@ -13398,7 +13398,7 @@ spec:
           type: RuntimeDefault
       containers:
         - name: cert-manager-controller
-          image: "quay.io/jetstack/cert-manager-controller:v1.20.3"
+          image: "quay.io/jetstack/cert-manager-controller:v1.21.0"
           imagePullPolicy: IfNotPresent
           args:
           - --v=2
@@ -13480,7 +13480,7 @@ spec:
           type: RuntimeDefault
       containers:
         - name: cert-manager-webhook
-          image: "quay.io/jetstack/cert-manager-webhook:v1.20.3"
+          image: "quay.io/jetstack/cert-manager-webhook:v1.21.0"
           imagePullPolicy: IfNotPresent
           args:
           - --v=2