add workflow to mirror cog-base images from r8.im to GHCR (#2871)
Add a workflow_dispatch workflow that copies cog-base images from r8.im
to ghcr.io/replicate/cog/cog-base using crane. Uses GITHUB_TOKEN for
GHCR authentication.
The list of tags to mirror is in integration-tests/cog-base-tags.txt
(4 CPU + 6 GPU base images used by integration tests).
Run this workflow from Actions > Mirror cog-base images > Run workflow
when new cog-base images are published or new tags are added.
