FEAT: GitHub actions for pushing cli image

.github/workflows/push-github.yml

@@ -0,0 +1,70 @@
+name: Publish image to GitHub Packages
+on:
+  push:
+    tags:
+      - v1.27.*
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: veraPDF/cli
+
+jobs:
+  publish:
+    if: github.repository == 'veraPDF/veraPDF-apps'
+    name: Build and push Docker image to GitHub packages
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@v2
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for GitHub
+        id: meta
+        uses: docker/metadata-action@v2
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - name: Calculate version
+        env:
+          TAG: ${{ github.ref_name }}
+        id: version
+        run: echo "::set-output name=version::${TAG##*.}"
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          file: Dockerfile
+          build-args: |
+            VERAPDF_VERSION=1.27
+            VERAPDF_MINOR_VERSION=${{ steps.version.outputs.version }}
+            VERAPDF_INSTALLER_FOLDER=develop
+          tags: ghcr.io/verapdf/cli:dev,${{ github.ref_name }}
+          labels: ${{ steps.meta.outputs.labels }}
+
+  send-notification:
+    runs-on: ubuntu-latest
+    needs: [checkout-and-build, merge]
+    if: |
+      always() &&
+      github.repository == 'veraPDF/veraPDF-apps' &&
+      (contains(needs.*.result, 'failure') ||
+      contains(needs.*.result, 'skipped') ||
+      contains(needs.*.result, 'cancelled'))
+    steps:
+      - name: Send notification if build or push failed
+        env:
+          SLACK_BOT_TOKEN: ${{ secrets.SLACK_NOTIFICATIONS_BOT_TOKEN }}
+        uses: voxmedia/github-action-slack-notify-build@v1
+        with:
+          channel_id: C03E3JJGLQL
+          status: FAILED
+          color: danger
+