Add GH action to push docker image

.github/workflows/docker-image.yml

@@ -0,0 +1,48 @@
+name: Publish Docker Image
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+env:
+  # Last fragment of identifier of the docker image
+  IMAGE_NAME: ${{ github.repository }}
+  # Group identifier of the docker image, typically ${{ github.repository_owner }} or ${{ github.repository }}
+  IMAGE_GROUP_NAME: ${{ github.repository_owner }}
+  MAIN_BRANCH_NAME: main
+
+jobs:
+  build-and-publish:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build docker image
+        run: docker build . --file Dockerfile --tag $IMAGE_NAME
+
+      - name: Log in to the Container registry
+        run: echo "${{ github.token }}" | docker login docker.pkg.github.com -u ${{ github.actor }} --password-stdin
+
+      - name: Push image
+        run: |
+          IMAGE_ID=docker.pkg.github.com/$IMAGE_GROUP_NAME/$IMAGE_NAME
+          # Change all uppercase to lowercase
+          IMAGE_ID=$(echo $IMAGE_ID | tr '[A-Z]' '[a-z]')
+          # Get branch name if merge to a branch
+          GIT_BRANCH_NAME=$(echo "${{ github.ref }}" | grep 'refs/heads/.*' | cut -d"/" -f 3)
+          # Get pull request id (e.g. "pr-123" from "/pulls/123")
+          PULL_REQUEST_ID=$(echo "${{ github.event.pull_request.number }}" | grep -v "^$" | sed 's/^/pr-/')
+          # Get tag id while strip "v" prefix (e.g. "1.2" from "v1.2")
+          TAG_ID=$(echo "${{ github.ref }}" | grep 'refs/tags/.*' | cut -d"/" -f 3 | sed -e 's/^v//')
+          # Version is either "git branch name"/"pull request id"/"tag id"                    
+          VERSION=${GIT_BRANCH_NAME:-${PULL_REQUEST_ID:-${TAG_ID}}}
+          # Use Docker `latest` tag convention
+          [ "$VERSION" == $MAIN_BRANCH_NAME ] && VERSION=latest
+          echo IMAGE_ID=$IMAGE_ID
+          echo VERSION=$VERSION
+          docker tag $IMAGE_NAME $IMAGE_ID:$VERSION
+          docker push $IMAGE_ID:$VERSION