Create action for docker build scripts

The PRs for changes to those scripts will be stored in the registry
of the user/organisation which forked or in our GitHub docker registry
if this branch is under the domjudge organization. Here we always build
against our latest version.

The GitLab code had the option to not push the latest tag, for when we
rebuild an older container, otherwise we always release against the
overwritten value or if nothing was provided against the latest released
tag (so which latest points to).

.github/workflows/build-domjudge-container-PR.yml

@@ -0,0 +1,56 @@
+name: 'Build domjudge container (PR)'
+
+on:
+  push:
+  pull_request_target:
+    branches:
+      - main
+
+env:
+  DOMJUDGE_VERSION: M.m.p
+
+jobs:
+  pr-domjudge:
+    if: ${{ github.repository != 'domjudge/domjudge-packaging' || github.ref != 'main' }} 
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+
+      - name: If needed overwrite the DOMJUDGE_VERSION for this run
+        run: |
+          if [ ${{ env.DOMJUDGE_VERSION }} != "M.m.p" ]; then
+            exit 0
+          fi
+          apk add jq curl
+          set -x
+            HUBURL="https://registry.hub.docker.com/v2/repositories/domjudge/domserver/tags"
+            TAG=$(curl $HUBURL|jq '.results | sort_by(.name) | .[length-2].name')
+            DJ_TAG=${TAG//\"}
+          set +x
+          echo "DOMJUDGE_VERSION=$DJ_TAG" >> $GITHUB_ENV
+
+      - name: Build the container
+        run: |
+          cd docker
+          set -x
+          sh ./build.sh "${{ env.DOMJUDGE_VERSION }}"
+          set +x
+
+      - name: Build and push
+        run: |
+          for IMG in domserver judgehost default-judgehost-chroot; do
+            docker push domjudge/$IMG:${{ env.DOMJUDGE_VERSION }}
+          done

.github/workflows/build-domjudge-container-release.yml

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+name: 'Build domjudge container (Release)'
+
+on:
+  push:
+  pull_request_target:
+    branches:
+      - main
+
+env:
+  DOMJUDGE_VERSION: M.m.p
+  DOMJUDGE_LATEST: true
+
+jobs:
+  release-domjudge:
+    if: ${{ github.repository == 'domjudge/domjudge-packaging' && github.ref == 'main' }} 
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ env.DOCKERHUB_USERNAME }}
+          password: ${{ env.DOCKERHUB_TOKEN }}
+
+      - name: If needed overwrite the DOMJUDGE_VERSION for this run
+        run: |
+          if [ ${{ env.DOMJUDGE_VERSION }} != "M.m.p" ]; then
+            exit 0
+          fi
+          if [ ${{ env.DOMJUDGE_LATEST }} == "false" ]; then
+            echo "I don't know which version to pick!"
+            exit 1
+          fi
+          apk add jq curl
+          set -x
+            HUBURL="https://registry.hub.docker.com/v2/repositories/domjudge/domserver/tags"
+            TAG=$(curl $HUBURL|jq '.results | sort_by(.name) | .[length-2].name')
+            DJ_TAG=${TAG//\"}
+          set +x
+          echo "DOMJUDGE_VERSION=$DJ_TAG" >> $GITHUB_ENV
+
+      - name: Build the container
+        run: |
+          cd docker
+          set -x
+          sh ./build.sh "${{ env.DOMJUDGE_VERSION }}"
+          set +x
+
+      - name: Build and push
+        run: |
+          for IMG in domserver judgehost default-judgehost-chroot; do
+            docker push domjudge/$IMG:${{ env.DOMJUDGE_VERSION }}
+            if [ ${{ env.DOMJUDGE_LATEST }} = "true" ]; then
+              docker tag domjudge/$IMG:${{ env.DOMJUDGE_VERSION }} domjudge/$IMG:latest
+              docker push domjudge/$IMG:latest
+            fi
+          done