Push docker images also to ghcr.io

Fixes #350.

Change-Id: Ifdb7e4e7fda46efd0ed9e760587033f52ff4a130

.github/workflows/docker-release.yml

@@ -1,4 +1,5 @@
-name: Create docker image(s) and push to docker hub
+name: Create docker image(s) and push to docker hub and ghcr.io
+# see https://docs.github.com/en/actions/publishing-packages/publishing-docker-images#publishing-images-to-docker-hub-and-github-packages
 
 on:
   push:
@@ -13,39 +14,48 @@ on:
 
 jobs:
   docker:
+    name: Push Docker image to multiple registries
     runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      contents: read
 
     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 DockerHub
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
-      - name: Calculate docker image tag
-        id: set-tag
-        run: |
-          case "${GITHUB_REF}" in
-              refs/heads/master|refs/heads/main)
-                  tag=latest
-                  ;;
-              refs/tags/*)
-                  tag=${GITHUB_REF#refs/tags/}
-                  ;;
-              *)
-                  tag=${GITHUB_SHA}
-                  ;;
-          esac
-          echo "::set-output name=tag::$tag"
+
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: |
+            awesometechnologies/synapse-admin
+            ghcr.io/${{ github.repository }}
+
       - name: Build and Push Tag
         uses: docker/build-push-action@v5
         with:
           context: .
           push: true
-          tags: "awesometechnologies/synapse-admin:${{ steps.set-tag.outputs.tag }}"
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
           platforms: linux/amd64,linux/arm64