[BUG] App name in metric is unknown_ go_ service

[kklinan]

Issue Description

Type: bug report

Describe what happened

sentinel-golang/exporter/metric/exporter.go

Lines 35 to 45 in 683c229

	func init() {
	exporter = newPrometheusExporter()
	host, _ = os.Hostname()
	if host == "" {
	host = "unknown"
	}
	app = config.AppName()
	pid = strconv.Itoa(os.Getpid())
	namespace = "sentinel_go"
	}

Since the above code (code 1) uses the init function and is executed before the following code (code 2), the app variable in code 1 is an error.

sentinel-golang/api/init.go

Lines 54 to 74 in 683c229

	func InitWithConfig(confEntity *config.Entity) (err error) {
	defer func() {
	if r := recover(); r != nil {
	var ok bool
	err, ok = r.(error)
	if !ok {
	err = fmt.Errorf("%v", r)
	}
	}
	}()
	err = config.CheckValid(confEntity)
	if err != nil {
	return err
	}
	config.ResetGlobalConfig(confEntity)
	if err = config.OverrideConfigFromEnvAndInitLog(); err != nil {
	return err
	}
	return initCoreComponents()
	}

[sczyh30]

Would you like to contribute a PR to fix it?