[concourse] Add service which targets prometheus port when prometheus metrics are enabled

[2color]

What this PR does / why we need it:

• Add a service that targets the prometheus metrics endpoint on the concourse webserver
• Use a service instead of prometheus.io labels as recommended for prometheus-operator (Update manifests to latest version of Prometheus Operator prometheus-operator/kube-prometheus#16 (comment))

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[2color]

/assign @william-tran

[william-tran]

Use a service instead of prometheus.io labels as recommended for prometheus-operator (prometheus-operator/kube-prometheus#16 (comment))

/cc @ebabani
Thoughts?

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In response to this:

Use a service instead of prometheus.io labels as recommended for prometheus-operator (prometheus-operator/kube-prometheus#16 (comment))

/cc @ebabani
Thoughts?

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[william-tran]

Is a distinct service for prometheus necessary if we do #6338 instead? @2color @richardalberto I'm not a prometheus ops expert so I'm not sure what the best practice is.

[2color]

Is a distinct service for prometheus necessary if we do #6338 instead? @2color @richardalberto I'm not a prometheus ops expert so I'm not sure what the best practice is.

#6338 should solve the problem. There's no real need for a distinct service. As long as the ingress doesn't expose it externally (which it doesn't as it specifies the port explicitly).

So I'm in favour of #6338