Expose metrics port when PrometheusMetricsEnabled set to true in Calico

[avdhoot]

Problem:
Currently PrometheusMetricsEnabled only start servings metrics on PrometheusMetricsPort . But Prometheus can not scrape it. This PR will expose that service so Prometheus can scrape it.
Sample config for Prometheus-operator

kind: PodMonitor
metadata:
  labels:
    k8s-app: calico-node
    monitoredBy: prometheus-infra
  name: calico-node
  namespace: kube-system
spec:
  podMetricsEndpoints:
  - interval: 30s
    path: /metrics
    port: metrics
  namespaceSelector:
    matchNames:
    - kube-system
  selector:
    matchLabels:
      k8s-app: calico-node

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Hi @avdhoot. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[hakman]

/ok-to-test

[hakman]

@avdhoot In the Calico docs I see that the ports are exposed with a service. Should this be added here also?
https://docs.projectcalico.org/maintenance/monitor/monitor-component-metrics#creating-a-service-to-expose-felix-metrics

[avdhoot]

@hakman we are using Prometheus pod discovery mechanism. I do not think we should create service only to expose metrics.

[hakman]

Thanks for the explanation and the contribution. I think will be appreciated by users.
/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: avdhoot, hakman

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