新增格式转换插件，新增http日志变量，调整json输出请求日志格式

node/http-context/proxy-agent.go

@@ -16,11 +16,16 @@ type requestAgent struct {
 	statusCode     int
 	status         string
 	responseLength int
+	responseBody   string
 	beginTime      time.Time
 	endTime        time.Time
 	hostAgent      *UrlAgent
 }
 
+func (a *requestAgent) ResponseBody() string {
+	return a.responseBody
+}
+
 func (a *requestAgent) ProxyTime() time.Time {
 	return a.beginTime
 }