Add build workflow

.github/build-push.yml

@@ -0,0 +1,37 @@
+name: build docker image & push to reg
+
+on:
+  pull_request:
+    types: [closed]
+    branches: [master]
+    paths: ["**"]
+
+jobs:
+  build-and-push:
+    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'CI:Build')
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Log in to DockerHub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: prep tags
+        id: vars
+        run: |
+          echo "COMMIT_SHA=$(git rev-parse --short HEAD)" >> $GITHUB_ENV
+          echo "IMAGE_NAME=${{ secrets.DOCKERHUB_USERNAME }}/geth-dev" >> $GITHUB_ENV
+
+      - name: build image
+        run: |
+          docker build -t $IMAGE_NAME:latest -t $IMAGE_NAME:$COMMIT_SHA .
+
+      - name: push image
+        run: |
+          docker push $IMAGE_NAME:latest
+          docker push $IMAGE_NAME:$COMMIT_SHA