add dockerfile and build action for docs

.forgejo/workflows/docs.yaml

@@ -0,0 +1,38 @@
+name: Build Antora Docs
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container: catthehacker/ubuntu:act-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ vars.CONTAINER_REGISTRY }}
+          username: ${{ secrets.CONTAINER_REGISTRY_USERNAME }}
+          password: ${{ secrets.CONTAINER_REGISTRY_TOKEN }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: docs/Dockerfile
+          push: true
+          tags: ${{ vars.CONTAINER_REGISTRY }}/${{ vars.CONTAINER_IMAGE_NAME_DOCS }}:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max