ci: run docker build on push to master

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

@@ -0,0 +1,48 @@
+name: Build and push docker image
+
+on:
+  workflow_dispatch:
+  workflow_call:
+  push:
+    branches:
+      - master
+
+jobs:
+  build_and_push_docker_image:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.3.0
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Determine tag
+        id: determine_tag
+        run: |
+          base_image="ghcr.io/dfe-digital/buying-for-schools-admin"
+          branch="${{ github.ref_name }}"
+          commit="$(echo $GITHUB_SHA | head -c7)"
+
+          if [ "$branch" == "master" ]; then
+            echo tags=${base_image}:${commit},${base_image}:latest >> $GITHUB_OUTPUT
+          else
+            echo tags=${base_image}:${commit},${base_image}:${branch} >> $GITHUB_OUTPUT
+          fi
+
+      - name: Build and push
+        uses: docker/build-push-action@v4
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.determine_tag.outputs.tags }}
+
+
+