[cherry-pick: release-v0.78.x] cleanup: replace GCS buckets with OCI buckets

[tekton-robot]

This is a cherry-pick of #3057

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Changes

This pull request updates Tekton release URLs throughout the documentation and scripts to use the new infra.tekton.dev domain instead of the previous storage.googleapis.com URLs. This PR also removes the release_yaml_oracle function since all components now use infra.tekton.dev

Migration to new Tekton release URL domain:

• Updated all references to Tekton release YAMLs in docs/install.md, tekton/setup-release-from-scratch.md, and hack/fetch-releases.sh to use https://infra.tekton.dev/tekton-releases/ instead of https://storage.googleapis.com/tekton-releases/.

Script cleanup and refactoring:

• Removed the release_yaml_oracle function from hack/fetch-releases.sh, as it is no longer needed with the unified URL format.
• Refactored the pruner release YAML fetching logic to use the standard release_yaml function, simplifying the code and ensuring consistency.

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Release Notes

NONE

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