Expose notifications-controller metrics to OpenShift monitoring

related conversation : https://coreos.slack.com/archives/CMP95ST2N/p1659532401868259

The notifications-controller exposes a set of metrics that can be collected by prometheus and displayed in a grafana dashboard 
see https://argo-cd.readthedocs.io/en/stable/operator-manual/notifications/monitoring/

The next step for our notifications-controller should be to follow this within the gitops-operator by creating required resources for that such as service, servicemonitor etc

Acceptance criteria

• Ensure operator creates service, servicemonitor to expose notifications metrics
• Test to ensure metrics are properly exposed and can be accessed via OpenShift monitoring stack