Using openshift-pipelines/setup-tektoncd Action

[otaviof]

Changes

Adopting openshift-pipelines/setup-tektoncd action in order to setup Tekton Pipelines and the Container Registry.

Preparing the release v2 with renamed inputs, following GitHub Action best practices and introducing feature_flags input to power up shipwright-io/triggers end-to-end testing using CustomRun instances (Tekton Custom Tasks).

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Set a kind label on this PR
• Release notes block has been filled in, or marked NONE

Release Notes

Renaming inputs to use underscore, instead of dashes. Please consider documentation to set up the inputs accordingly.

Introducing `feature_flags` to set Tekton Pipeline feature flags toggles.

[openshift-ci]

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[otaviof]

/assign @SaschaSchwarze0