publish docker images to GitHub Container Registry (#1453)

The goal is to use GHCR to replace Google Container Registry (GCR) for
future versions of Scorecard Action releases. These workflows will build
two types of images:

  1. Release images, which are tagged following a v1.2.3 pattern. These
  container images will be retained indefinitely.
  2. Per-commit images for each push to main. These images are used when
     testing the action, and will be removed after a week.

Signed-off-by: Spencer Schrock <sschrock@google.com>

.github/workflows/ghcr-retention.yml

@@ -0,0 +1,22 @@
+name: Delete untagged GHCR images
+on:
+  schedule:
+    - cron:  '17 10 * * TUE' # Tuesday morning at 10:17 UTC
+  workflow_dispatch:
+
+permissions: {}
+
+jobs:
+  delete-untagged:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - uses: actions/delete-package-versions@e5bc658cc4c965c472efe991f8beea3981499c55 # v5.0.0
+        with: 
+          package-name: 'scorecard-action'
+          package-type: 'container'
+          # keep official releases
+          delete-only-untagged-versions: 'true'
+          # 'latest' counts as a tag, so this won't break the e2e tests
+          min-versions-to-keep: 0

.github/workflows/ghcr.yml

@@ -0,0 +1,59 @@
+name: Publish GitHub Container Registry
+on:
+  push:
+    branches: ['main']
+    tags:
+      - v*
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+permissions:
+  contents: read
+
+jobs:
+  build-and-push-image:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      attestations: write
+      id-token: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938 # v4.2.0
+      - name: Log in to the Container registry
+        uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@8e5442c4ef9f78752691e2d8f8d19755c6f78e81 # v5.5.1
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          # pushes to the default branch get labeled latest, otherwise use tag name
+          tags: |
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=ref,event=tag
+
+      - name: Build and push Docker image
+        id: push
+        uses: docker/build-push-action@4f58ea79222b3b9dc2c8bbdd6debcef730109a75 # v6.9.0
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+
+      - name: Generate artifact attestation
+        uses: actions/attest-build-provenance@1c608d11d69870c2092266b3f9a6f3abbf17002c # v1.4.3
+        # only publish attestation for our release builds
+        if: startsWith(github.ref, 'refs/tags/v')
+        with:
+          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
+          subject-digest: ${{ steps.push.outputs.digest }}
+          push-to-registry: true