Fix metrics port expose issue for triggers eventlistener

[savitaashture]

Changes

Metrics related changes introduced as part of #1061 and because of those changes we are facing below issues when we create Knative Service using customeResources

1. when we apply custom-resource example EL fail with below error

Warning  InternalError    15s (x14 over 56s)  EventListener  admission webhook "validation.webhook.serving.knative.dev" denied the request: validation failed: More than one container port is set: spec.template.spec.containers[0].ports
Only a single port is allowed

2. Knative Serving adds queue-proxy container along with EL container and Knative itself handles metrics on 9090 port for queue-proxy and because of that we face already bind error

{"severity":"ERROR","timestamp":"2021-05-11T09:28:00.588588485Z","logger":"queueproxy","caller":"queue/main.go:228","message":"Failed to bring up queue-proxy, shutting down.","commit":"813aa65","knative.dev/key":"dtest/el-github-knative-listener-00001","knative.dev/pod":"el-github-knative-listener-00001-deployment-fc8fb5cbc-xbqqv","error":"metrics server failed to listen: listen tcp :9090: bind: address already in use","stacktrace":"main.main\n\tknative.dev/serving/cmd/queue/main.go:228\nruntime.main\n\truntime/proc.go:204"}

The PR solves above issues and exposes metrics on 9000 port

Fixes #1090

/cc @jmcshane @dibyom

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Release Notes

Triggers exposes metrics on 9000 port 

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.0%	79.1%	0.1

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.0%	79.1%	0.1

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.0%	79.1%	0.1

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.0%	79.1%	0.1

[dibyom]

I tried to quickly dig down into where we were actually setting up the metrics server port to see if there was an easier way to do this but failed. One idea: Would it be possible to just set the port on the defaultObservabilityConfig()

[dibyom]

How about something like this:

	updateFunc, err := metrics.UpdateExporterFromConfigMapWithOpts(ctx, exp, logger)
	if err != nil {
		logger.Fatal("Failed to create metrics exporter update function", zap.Error(err))
	}
	configMapWatcher.Watch(metrics.ConfigMapName(), updateFunc)

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.1%	78.6%	-0.4

[savitaashture]

I tried to quickly dig down into where we were actually setting up the metrics server port to see if there was an easier way to do this but failed. One idea: Would it be possible to just set the port on the defaultObservabilityConfig()

Used METRICS_PROMETHEUS_PORT env to set the port as part of controller.yaml

[savitaashture]

This change is not part of issue
But its a duplicate code so just removed

[jmcshane]

outside of the gocritic issue, this looks good to me

/lgtm

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.1%	78.6%	-0.4

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/v1alpha1/eventlistener/eventlistener.go	79.1%	78.6%	-0.4

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dibyom

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[dibyom]

/lgtm