Enable Prometheus metrics for deployed Ingresses

Follow-up of https://gitlab.com/gitlab-org/gitlab-ce/issues/35958.

We already can install ingress in Kubernetes clusters, but we need to add the additional configuration parameters for enabling Prometheus monitoring on the ingress.

1. Annotations to inform Prometheus to scrape it.(https://gitlab.com/charts/charts.gitlab.io/blob/master/charts/gitlab-omnibus/templates/load-balancer/nginx/daemonset.yaml#L11)
2. Enable metrics. (https://gitlab.com/charts/charts.gitlab.io/blob/master/charts/gitlab-omnibus/templates/load-balancer/nginx/configmap.yaml#L9)
3. ContainerPort of 10254. (https://gitlab.com/charts/charts.gitlab.io/blob/master/charts/gitlab-omnibus/templates/load-balancer/nginx/daemonset.yaml#L40)