Prepare release pipeline for ghcr.io

[afrittoli]

Changes

To reduce CI spending, we're in the process of moving all new release to ghcr.io - https://github.com/tektoncd/plumbing/issues/2157

This prepares the release pipeline for that switch (which will require a PR in the plumbing repo).

This PR also aligns the pipeline with some other small improvements already adopted by other projects:

• use remote resolution for tasks
• only run build and tests when requested - it will be disabled by default on nightly builds

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• [x] Has Docs included if any changes are user facing
• [x] Has Tests included if any functionality added or changed
• [x] Follows the commit message standard
• [x] Meets the Tekton contributor standards (including functionality, content, code)
• [x] Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings)
• [ ] Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lcarva

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