add ConfigMap and Service for observability

[avinal]

Changes

• this PR adds ConfigMap for configuring metrics and a Service to expose the port

Submitter Checklist

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• Has Docs included if any changes are user facing
• Has Tests included if any functionality added or changed
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  functionality, content, code)
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings)
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Release Notes

- Metrics can be accessed by exposing the Service `tekton-chains-controller`
- adds a ConfigMap for configuring metrics

[tekton-robot]

Hi @avinal. Thanks for your PR.

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[lcarva]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lcarva

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[wlynch]

/ok-to-test
/lgtm