Add Event Count for EventListener Metrics

[khrm]

Added metrics to add count for number of events received at sink

Changes

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• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
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Release Notes

Added a new metrics called event_count for events received at EventListener Sink

[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/sink/metrics.go	78.6%	79.1%	0.5

[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/sink/metrics.go	78.6%	79.1%	0.5

[dibyom]

Looks good!

Can we update the docs too? https://github.com/tektoncd/triggers/blob/main/docs/eventlisteners.md#configuring-metrics-for-eventlisteners

[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/sink/metrics.go	78.6%	79.1%	0.5

[khrm]

Updated docs with new metrics, @dibyom @savitaashture

[khrm]

/test pull-tekton-triggers-integration-tests

[dibyom]

Thank you!
/approve
/lgtm

[tekton-robot]

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