ci: checking artifacts

[nsingla]

Changes Made

1. Replaced the artifact download step (image-builds-with-cache.yml:71-77):
   - Removed actions/download-artifact@v4 which actually downloaded artifacts
   - Added nsingla/github-actions/github-artifacts@main with operation 'check' to only verify if artifacts exist
2. Updated the Docker Buildx step condition (image-builds-with-cache.yml:82):
   - Changed from steps.artifact-download.outcome == 'failure'
   - To steps.artifact-check.outputs.artifact-exists == 'false'
   - Now it runs when the artifact does NOT exist (when we need to build)
3. Removed the artifact cleanup step (previously lines 79-85):
   - Since we're no longer downloading artifacts, we don't need to clean them up
   - The action only checks for existence, doesn't actually download anything

Benefits of This Change

• More efficient: No longer downloads artifacts unnecessarily just to check if they exist
• Cleaner workflow: Removes the download-then-delete pattern
• Better logic: Uses a proper boolean check (artifact-exists == 'false') instead of relying on step outcomes
• Reduced network usage: Only queries artifact metadata instead of downloading full files

Checklist:

• You have signed off your commits
• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

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[google-oss-prow]

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