no default metric (#199)

Co-authored-by: zhoushuguang <zhoushuguang@xiaoheiban.cn>

core/prometheus/config.go

@@ -1,7 +1,7 @@
 package prometheus
 
 type Config struct {
-	Host string `json:",default=127.0.0.1"`
+	Host string `json:",optional"`
 	Port int    `json:",default=9101"`
 	Path string `json:",default=/metrics"`
 }

core/service/serviceconf.go

@@ -21,7 +21,7 @@ type ServiceConf struct {
 	Log        logx.LogConf
 	Mode       string            `json:",default=pro,options=dev|test|pre|pro"`
 	MetricsUrl string            `json:",optional"`
-	Prometheus prometheus.Config
+	Prometheus prometheus.Config `json:",optional"`
 }
 
 func (sc ServiceConf) MustSetUp() {