Add a CI workflow for ETOS suite starter (#25)

This workflow will run when a PR is merged, it will
build the docker image with the current SHA as tag and
push it to the registry.
After the image has been pushed it will update the image
version in the manifests and push them to main.

.github/workflows/build-push.yml

@@ -0,0 +1,45 @@
+name: Build and push
+
+on:
+  pull_request:
+    branches: [ "main" ]
+    types:
+      - closed
+  workflow_dispatch:
+
+jobs:
+  build:
+    if: github.event.pull_request.merged == true
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: Build app image
+      run: docker build . --tag image
+
+    - name: Log into registry
+      run: echo "${{ secrets.REGISTRYPASSWORD }}" | docker login registry.nordix.org -u ${{ secrets.REGISTRYUSERNAME }} --password-stdin
+
+    - name: Push app image
+      id: image
+      run: |
+        IMAGE_ID=registry.nordix.org/eiffel/${{ github.repository }}
+        # Strip git ref prefix from version
+        VERSION=$(echo "${{ github.ref }}" | sed -e 's,.*/\(.*\),\1,')
+        # Strip "v" prefix from tag name
+        [[ "${{ github.ref }}" == "refs/tags/"* ]] && VERSION=$(echo $VERSION | sed -e 's/^v//')
+        # Use Docker `latest` tag convention
+        [ "$VERSION" == "main" ] && VERSION=$(echo ${{ github.sha }} | cut -c1-8)
+        echo IMAGE_ID=$IMAGE_ID
+        echo VERSION=$VERSION
+        docker tag image $IMAGE_ID:$VERSION
+        docker push $IMAGE_ID:$VERSION
+        echo $IMAGE_ID:$VERSION
+        echo "::set-output name=version::$VERSION"
+    - name: Update manifests
+      uses: fjogeleit/yaml-update-action@main
+      with:
+        valueFile: 'manifests/base/deployment.yaml'
+        propertyPath: 'spec.template.spec.containers[0].image'
+        value: registry.nordix.org/eiffel/etos-suite-starter:${{ steps.image.outputs.version }}
+        commitChange: true
+        message: Updating manifest image to version ${{ steps.image.outputs.version }}