Build docker image for each PR (#300)

This builds a docker image for each PR and then one for the release
tagged as :latest.

.github/workflows/docker-build-push.yml

@@ -0,0 +1,56 @@
+name: Create and publish a Docker image
+
+on:
+  workflow_call:
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push-image:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Figure out branch name
+        shell: bash
+        run: echo "branch=${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}}" >> $GITHUB_OUTPUT
+        id: extract_branch
+      - name: Determine docker image tag
+        shell: bash
+        id: determine_tag
+        run: |
+          if [[ "${{ github.ref }}" == "refs/heads/main" ]]; then
+            echo "tag=latest" >> $GITHUB_OUTPUT
+          else
+            echo "tag=${{ steps.extract_branch.outputs.branch }}" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+      # Buildx for caching
+      - uses: docker/setup-buildx-action@v3
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ steps.determine_tag.outputs.tag }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max