[CHORE] Add support for a custom logger

[m-t-a97]

Synopsis

Currently Authula has a default logger set to use slog by default but developers want the ability to inject their own custom logger such as: zap, zerolog, logrus and others.

This ticket therefore suggests refactoring the logger config within the main config to allow developers in Library Mode to be able to provide a custom logger via a Logger interface to keep things simple and maintainable.

Implementation

For example:

interface Logger {
  Debug(msg string, args ...any)
  Info(msg string, args ...any)
  Warn(msg string, args ...any)
  Error(msg string, args ...any)
}