fix: load log configuration from config file

[jeengbe]

I'm relatively new to Go, so please bear with me :)

The default logf.Log returns a delegatingLogSink whose implementation can (crucially) only be overwritten once. So the first time the logger is configured with _ = setLogger(&opts, "", ""), that call only includes CLI flags, but not options loaded from the configuration file.

Instead, this PR hard-wires the setupLog logger to use zap.New(zap.UseDevMode(true)), which ensures that all setup/teardown logs remain visible while allowing the later real setLogger to replace the remaining application loggers from ctrl.Log.

This has two side effects:

• The setup logger no longer respects CLI flags for log level/format
• Potential callers that don't bind to setupLog explicitly don't print logs before setLogger is called

I don't see a clean way around that second catch-22. Given that the global delegating logger instance may only be rebound once and loading the configuration file itself may possibly emit logs (I did not find that it does, but it seems not to be prohibited_ from doing so), the only clean fix I see is to not use the global logger from the pre-configuration pass?