support customize default log field name

[dlsrb6342]

• we cannot change http, grpc default field name.
• How about adding LogFieldName for customizing log field name?

// http_option.go
var DefaultHttpLogFieldName = &HttpLogFieldName{
	Protocol:      "protocol",
	Path:          "path",
	Status:        "status",
	UserAgent:     "ua",
	RequestedTime: "time",
	ElapsedTime:   "elapsed(ms)",
	QueryString:   "qs",
	ClientIp:      "client-ip",
}

type HttpLogFieldName struct {
	Protocol      string
	Path          string
	Status        string
	UserAgent     string
	RequestedTime string
	ElapsedTime   string
	QueryString   string
	ClientIp      string
}

func WithLogFieldName(logFieldName HttpLogFieldName) httpOption {
	return func(cfg *httpConfig) {
		cfg.logFieldName = logFieldName
	}
}

// http.go
e := le.l.Log().
	Str(le.cfg.logFieldName.Protocol, "http").
	Str(le.cfg.logFieldName.Path, le.r.URL.Path).
	Str(le.cfg.logFieldName.Status, strconv.Itoa(le.ww.Status())).
	Str(le.cfg.logFieldName.UserAgent, le.r.UserAgent()).
	Str(le.cfg.logFieldName.RequestedTime, t.UTC().Format(time.RFC3339Nano)).
	Dur(le.cfg.logFieldName.ElapsedTime, time.Since(t))