Provide a way to hook into logging for this gem

[codenamev]

Is your feature request related to a problem? Please describe.
A common pattern for gems is to provide a configurable logger that can be used throughout the library to broadcast useful information. An example of the need here.

Describe the solution you'd like
Ideally, a logger method be added to the root namespace so it can be accessed from any part of the library. The logger would return an instance of Ruby's Logger class (or a descendent), and this would be configurable within OpenAI.configure

[alexrudall]

Thanks @codenamev, v6.3 adds a way to add a logger via Faraday's middleware - see README