Option to set io.Writer on middleware initialization

[mingalevme]

Problem:

In case of JSON logging you must set writer every request (cause WithLogger-fn is executed every request):

// Example of JSON format log
r.GET("/json", logger.SetLogger(
  logger.WithLogger(func(_ *gin.Context, l zerolog.Logger) zerolog.Logger {
    return l.Output(gin.DefaultWriter).With().Logger()
  }),
), func(c *gin.Context) {
  c.String(http.StatusOK, "pong "+fmt.Sprint(time.Now().Unix()))
})

So the command return l.Output(gin.DefaultWriter).With().Logger() is also executed every request.

Logger.Output() method deep clones Logger with entire context:

// github.com/rs/zerolog@v1.34.0/log.go
// Output duplicates the current logger and sets w as its output.
func (l Logger) Output(w io.Writer) Logger {
	l2 := New(w)
	l2.level = l.level
	l2.sampler = l.sampler
	l2.stack = l.stack
	if len(l.hooks) > 0 {
		l2.hooks = append(l2.hooks, l.hooks...)
	}
	if l.context != nil {
		l2.context = make([]byte, len(l.context), cap(l.context))
		copy(l2.context, l.context)
	}
	return l2
}

So in case of JSON logging runtime deep clones logger with the entire context every request. I'm sure it's not a desired behaviour for the majority of the developes.