Create Docker image for GHA GFM builds

.github/workflows/build-docker.yml

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+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Docker Image
+description: "Create Docker image for GHA GFM builds"
+
+on:
+  # allow direct trigger
+  workflow_dispatch:
+  push:
+    paths:
+      - 'Dockerfile'
+      - 'requirements.txt'
+      - 'bin/**'
+      - 'plugins/**'
+      - '.github/workflows/build-docker.yml'
+
+env:
+  REGISTRY: ghcr.io
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Image prefix (force lower case)
+        run: |
+          echo "IMAGE_PREFIX=$(echo ${{ env.REGISTRY }}/${{ github.repository }} | tr '[A-Z]' '[a-z]')" >>$GITHUB_ENV
+      - name: Checkout
+        uses: actions/checkout@44c2b7a8a4ea60a981eaca3cf939b5f4305c123b # v4.1.5
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@d70bba72b1f3fd22344832f00baa16ece964efeb # v3.3.0
+      - name: Login to Docker Hub
+        uses: docker/login-action@e92390c5fb421da1463c202d546fed0ec5c39f20 # 3.1.0
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build and push main image
+        uses: docker/build-push-action@2cdde995de11925a030ce8070c3d77a52ffcf1c0 # v5.3.0
+        with:
+          context: .
+          file: Dockerfile
+          push: true
+          tags: ${{ env.IMAGE_PREFIX }}:latest