Update Docker CI workflow to build and push image

Author: Warren-SJ

.github/workflows/docker-image.yml

@@ -0,0 +1,36 @@
+name: Build and push Docker image
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+
+      - name: Build with Maven
+        run: mvn -DskipTests package
+        working-directory: backend
+
+      - name: Build Docker image
+        run: docker build -t ${{ secrets.DOCKERHUB_USERNAME }}/transformer-tracker:latest
+        working-directory: backend
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Push image
+        run: docker push ${{ secrets.DOCKERHUB_USERNAME }}/transformer-tracker:latest