[EKS] [Community Addon cert-manager]: Expose Prometheus values

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**Tell us about your request**
Prometheus metrics are enabled and available by default when installing the addon.
The Prometheus values are not exposed in the addon configuration values.
Can these be exposed.

The values are set here in the [cert-manager helm chart](https://github.com/cert-manager/cert-manager/blob/master/deploy/charts/cert-manager/values.yaml#L514):

```
prometheus:
servicemonitor:
enabled: true
```

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I want to monitor cert-manager using Prometheus and graph metrics in Grafana.

**Are you currently working around this issue?**
Yes, by manually creating a Service Monitor.

cert_manager_service_monitor.yaml

```yaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
labels:
app: cert-manager
app.kubernetes.io/component: controller
app.kubernetes.io/instance: cert-manager
app.kubernetes.io/name: cert-manager
name: cert-manager
namespace: cert-manager
spec:
endpoints:
- honorLabels: false
interval: 60s
path: /metrics
scrapeTimeout: 30s
targetPort: 9402
namespaceSelector:
matchNames:
- cert-manager
selector:
matchExpressions:
- key: app.kubernetes.io/name
operator: In
values:
- cainjector
- cert-manager
- webhook
- key: app.kubernetes.io/instance
operator: In
values:
- cert-manager
- key: app.kubernetes.io/component
operator: In
values:
- cainjector
- controller
- webhook

```

Start with the cert-manager Helm chart's deploy/charts/cert-manager/values.yaml, especially the prometheus.servicemonitor settings, and compare those values with the EKS community addon configuration. Done means the Prometheus values are exposed through the addon configuration so users do not need to create a ServiceMonitor manually.

Written by the indexing model from the issue text.