feat: automate releases with Pipelines-as-Code

[vdemeester]

Summary

Automate releases using Pipelines-as-Code (PAC), following the pattern already implemented in other tektoncd repositories.

What needs to happen

1. Repository side: Add .tekton/release.yaml and .tekton/release-patch.yaml PAC trigger files (see tektoncd/pipeline or tektoncd/chains for reference)
2. Plumbing side: Add a PAC Repository CR in tektoncd/plumbing under tekton/cd/pipelines-as-code/overlays/oci-ci-cd/repositories/ (see existing CRs for pipeline, chains, pruner, operator, cli as examples)

References

Already completed in:

• tekton: automate releases with Pipelines-as-Code pipeline#9671
• tekton: automate releases with Pipelines-as-Code chains#1656
• tekton: automate releases with Pipelines-as-Code pruner#246
• tekton: automate releases with Pipelines-as-Code operator#3322

In progress:

• feat: automate releases with Pipelines-as-Code cli#2795

[rajnish-cloudbees]

I'd like to pick this up. I'll follow the pattern from tektoncd/pipeline#9671 — add .tekton/release.yaml and .tekton/release-patch.yaml here, plus a companion PR to tektoncd/plumbing for the PAC Repository CR. Will open both PRs together.