feat: Add the possibility to set log verbosity programatically

[philippart-s]

Hi,

If I'm not mistaken, the only way to configure the log detail level today is to set the OPENAI_LOG environment variable before launching the application.

I think it would be practical to add a way in the client to enable logging, for example:

OpenAIClient client = OpenAIOkHttpClient.builder()
            .apiKey(System.getenv("xxx"))
            .baseUrl(System.getenv("xxx"))
            .logRequest(true) // or logLevel(Log.DEBUG) 
            .build();