Swap image and provenance registries

[saisatishkarra]

@ianlewis / @laurentsimon Here is the PR that does:

• image pushed to GHCR.io
• provenance pushed to docker.io with username laurentsimon (hardcoded) and ${{ secrets.E2E_DOCKER_HUB_TOKEN }}
• Both registries expect the slsa-framework/<workflow-name> as the namespace/repository to exist
• Doesn't support any deletion of images

[laurentsimon]

Let me run it and see if it works