Update deployment configuration for main branch

.github/workflows/main.yaml

@@ -1,7 +1,12 @@
 name: Fly Deploy
-on: [push]
+on:
+  push:
+    branches:
+      - main
 env:
   FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}
+  PRODUCTION_URL: 'https://html-reprs.fly.dev/docs'
+  STAGING_URL: 'https://html-reprs.fly.dev/docs'
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -11,6 +16,9 @@ jobs:
   deploy:
     name: Deploy app
     runs-on: ubuntu-latest
+    environment:
+      name: ${{ github.ref == 'refs/heads/main' && 'production' || 'staging' }}
+      url: ${{ github.ref == 'refs/heads/main' && env.PRODUCTION_URL || env.STAGING_URL }}
     steps:
       - uses: actions/checkout@v4
       - uses: superfly/flyctl-actions/setup-flyctl@master