GitHub Actions: add workflow to build Docker images for CI

.github/workflows/docker_builds.yml

@@ -0,0 +1,83 @@
+name: Docker test image builds
+
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - 'docker/**'
+  workflow_dispatch:
+
+concurrency:
+  group: docker-builds
+
+env:
+  REGISTRY: ghcr.io
+  NAMESPACE: fish-ci
+
+jobs:
+  docker-build:
+    permissions:
+      contents: read
+      packages: write
+      attestations: write
+      id-token: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: alpine
+          - os: ubuntu-latest
+            target: centos9
+          - os: ubuntu-latest
+            target: fedora
+          - os: ubuntu-latest
+            target: focal-32bit
+          - os: ubuntu-24.04-arm
+            target: focal-arm64
+          - os: ubuntu-latest
+            target: focal
+          - os: ubuntu-24.04-arm
+            target: jammy-armv7-32bit
+          - os: ubuntu-latest
+            target: jammy-asan
+          - os: ubuntu-latest
+            target: jammy-tsan
+          - os: ubuntu-latest
+            target: jammy
+          - os: ubuntu-latest
+            target: noble
+          - os: ubuntu-latest
+            target: opensuse-tumbleweed
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v5
+      -
+        name: Login to Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      -
+        name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@9ec57ed1fcdbf14dcef7dfbe97b2010124a938b7
+        with:
+          images: ${{ env.REGISTRY }}/${{ github.repository_owner }}/${{ env.NAMESPACE }}/${{ matrix.target }}
+          flavor: |
+            latest=true
+      -
+        name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: docker/context
+          push: true
+          file: docker/${{ matrix.target }}.Dockerfile
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}