ci: push nightly builds (#6517)

.github/workflows/docker.yml

@@ -0,0 +1,22 @@
+name: Nightly Builds
+# Nightly Builds rebuilds the simapp docker image Monday - Friday at midnight
+# and pushes the image to https://hub.docker.com/r/interchainio/simapp/tags
+on:
+  schedule:
+    - cron: "0 0 * * 1-5" # deploy at midnight Monday - Friday
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@master
+      - name: Get current date
+        id: date
+        run: echo "::set-output name=date::$(date +'%Y-%m-%d')"
+      - name: Publish to Docker Hub
+        uses: docker/build-push-action@v1.1.0
+        with:
+          repository: interchainio/simapp
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+          tags: nightly-${{ steps.date.outputs.date }}