perf: the config.Writer should be used in preference in elog Build

[laojianzi]

defaultConfig() has been read Writer from env

ego/core/elog/config.go

Line 55 in ee9e1c3

Writer: eapp.EgoLogWriter(),

so we should give preference to config.Writer

---

ego/core/elog/container.go

Lines 58 to 60 in 435ef98

	if eapp.EgoLogWriter() == "stderr" {
	c.config.fields = append(c.config.fields, FieldLogName(c.config.Name))
	}

If we don't set env but do set config, the Writer here will be ignored