Add labels for images on ArtifactHub

[ledif]

From ublue-os/main#720 (comment).

Current labels with skopeo inspect --config docker://ghcr.io/winblues/vauxite:latest | jq '.config.Labels':

{
  "containers.bootc": "1",
  "io.artifacthub.package.readme-url": "https://raw.githubusercontent.com/blue-build/cli/main/README.md",
  "org.blue-build.build-id": "5bcf5c53-8d4a-4d35-b521-883943e2478f",
  "org.opencontainers.image.base.digest": "sha256:800f08eb77b451a7a3b64d09d6b233471637b470bcbdaf5a7a111f6f1dad3976",
  "org.opencontainers.image.base.name": "quay.io/fedora-ostree-desktops/xfce-atomic:41",
  "org.opencontainers.image.created": "2025-03-12T06:25:34.884593830+00:00",
  "org.opencontainers.image.description": "A modern lightweight atomic desktop",
  "org.opencontainers.image.source": "https://github.com/winblues/vauxite",
  "org.opencontainers.image.title": "vauxite",
  "org.opencontainers.image.version": "41.20250312.0",
  "ostree.bootable": "true",
  "ostree.commit": "aa03bd55ce88b7218958b97554c26e28a658571d2ba778ee560ffb3f11849788",
  "ostree.final-diffid": "sha256:12787d84fa137cd5649a9005efe98ec9d05ea46245fdc50aecb7dd007f2035b1",
  "ostree.linux": "6.13.5-200.fc41.x86_64",
  "quay.expires-after": "4w",
  "rpmostree.inputhash": "faa50147fde3f7ac15941d049460d7dcf6b72b8d605e2cd301651b37d093c813"
}

Labels that we need:

    LABELS=()
    LABELS+=("--label" "io.artifacthub.package.readme-url=https://raw.githubusercontent.com/winblues/vauxite/refs/heads/main/README.md")
    LABELS+=("--label" "io.artifacthub.package.logo-url=https://avatars.githubusercontent.com/u/200125887?s=200&v=4")
    LABELS+=("--label" "io.artifacthub.package.deprecated=false")
    LABELS+=("--label" "io.artifacthub.package.keywords=bootc,fedora,aurora,ublue,universal-blue")
    LABELS+=("--label" "io.artifacthub.package.maintainers=[{\"name\": \"ledif\", \"email\": \"adam@fidel.cloud\"}]")

Resources:

• feat: automatically adding artifacthub-compatible metadata to user images blue-build/cli#342
• https://github.com/detiber/beardy-os/blob/main/.github/workflows/artifacthub-repo.yml