Store appsettings.json in a standard location

[jrial]

I noticed that the settings file is stored in whichever folder you happen to be in when you run the chat-gpt binary. Every OS has its own concept of "location where user specific application settings should be stored", so it would be better to use those. Otherwise, users would need to enter their API key every time they start the application from a different folder, and their filesystem would be littered with config files.

When doing so, best also rename the file. The name appconfig.json is generic and doesn't tell me which app the config belongs to. It could also potentially clash with another app that also doesn't name their configs appropriately.