ci: add docker build action

.github/workflows/docker_build.yml

@@ -0,0 +1,26 @@
+name: Docker Image CI
+
+on:
+  push:
+    tags:
+      - "v*.*.*"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out code into the Go module directory
+        uses: actions/checkout@v3
+
+      - name: Set build tag as env var
+        run: echo "TAG=${GITHUB_REF#refs/*/v}" >> $GITHUB_ENV
+
+      - name: Docker login
+        run: docker login -u ${{ secrets.DOCKERHUB_USERNAME }} -p ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build the Docker image
+        run: docker build . --file Dockerfile --tag ${{ secrets.DOCKERHUB_USERNAME }}/blackjackbot:latest --tag ${{ secrets.DOCKERHUB_USERNAME }}/blackjackbot:${{ env.TAG }}
+
+      - name: Push the Docker image
+        run: docker push ${{ secrets.DOCKERHUB_USERNAME }}/blackjackbot --all-tags