ci: add action to build and push docker image

.github/workflows/docker-image.yml

@@ -0,0 +1,28 @@
+name: ci
+
+on:
+  push:
+    tags:
+      - "*"
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: ghcr.io/tendermint/faucet:latest,ghcr.io/tendermint/faucet:${GITHUB_REF#refs/*/}