Change the way of passing customLevels in code level

Due to pino handle customLevels as object often people will try to use like that in pino-pretty, so receiving a object instead of a string when using in code level as a transporter in pino would improve the understanding and use of the lib.

To work like that, instead of transforming the object to string and keeping two instances who had the same value but in different types:

const levels = {
  http: 10,
  info: 30,
  debug: 35,
  warn: 40,
  normal_error: 50,
  fatal_error: 60,
}

const log = pino(
  {
    customLevels: levels,
    useOnlyCustomLevels: true,
    level: 'http'
  },
  pretty({
  colorize: true,
  levelFirst: true,
  customLevels: levels,
  })
);

pinojs / pino-pretty

Change the way of passing customLevels in code level #399