Allow bypassing app router with FARSIDE_NO_ROUTER

Setting the aforementioned env var skips creation of the app router,
which is useful for running update.exs when the main app is already
running (otherwise there's a port conflict).

config/config.exs

@@ -1,6 +1,7 @@
 import Config
 
 config :farside,
+  port: 4001,
   redis_conn: "redis://localhost:6379",
   update_file: ".update-results",
   service_prefix: "service-",