config: set admin credentials via env vars

docker-compose.yml

@@ -8,6 +8,8 @@ services:
       - xdl_data:/app/data
     environment:
       - DATABASE_URL=sqlite+aiosqlite:///./data/xdl.db
+      - ADMIN_USERNAME=admin
+      - ADMIN_PASSWORD=Qweewqzzx1
 
   frontend:
     build: ./frontend