additionally upload ISOs in PRs via oras to container registry

[renner0e]

artifacts are super slow to download sometimes, ghcr is usually faster, let's upload our ISOs there.

ghcr.io/get-aurora-dev/iso/nameoftheiso:latest or we could do ...iso/aurora-testing-nvidia-open:x86_64

That means PRs should be more tightly reviewed as every push will upload to ghcr

We should also

• clean them up https://github.com/ublue-os/aurora/blob/main/.github/workflows/clean.yml
• sign them with cosign