Add custom asciidoctor image CI build

.gitea/workflows/image.yaml

@@ -0,0 +1,43 @@
+# Based on https://github.com/riscv/riscv-docs-base-container-image/blob/main/.github/workflows/build.yaml
+name: Build and publish custom Asciidoctor image
+
+on:
+  push:
+    branches: [master]
+    paths:
+      - "docker/Dockerfile"
+
+jobs:
+  build:
+    name: Build and push to Container Registry
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: git.elyanpoujol.fr
+          username: ${{ secrets.CONTAINER_REGISTRY_USERNAME }}
+          password: ${{ secrets.CONTAINER_REGISTRY_TOKEN }}
+
+      - name: Get Current Date
+        run: echo "NOW=$(date +'%m%d%Y')" >> "$GITEA_ENV"
+
+      - name: Build image and push to Docker Hub
+        uses: docker/build-push-action@v6
+        with:
+          context: ./docker
+          platforms: linux/amd64,linux/arm64
+          tags: |
+            docker-asciidoctor-wavedrom:${{ github.sha }}
+            docker-asciidoctor-wavedrom:latest
+          push: true