fly: add action and config for fly deployment

.github/workflows/deploy.yml

@@ -0,0 +1,20 @@
+name: deploy
+on:
+  push:
+    branches:
+      - "main"
+
+concurrency:
+  group: production
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    environment: production
+    steps:
+    - uses: actions/checkout@v3
+    - uses: superfly/flyctl-actions/setup-flyctl@master
+    - run: flyctl -c etc/fly.toml deploy --remote-only
+      env:
+        FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}