Fixes after review

- Maybe it could be rephrased to "attribute name prefixed with X-Attribute-"
- Maybe it worth renaming to userAttributeHeaderPrefix
- Requirement for having only one file uploaded at a time has to be reflected in documentation.
- Maybe this should be reflected in doc
- I'm not sure if missing timestamp attribute should be forced on gateway level. Normally it should be set by app and there should be a way not to set it.

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

settings.go

@@ -54,9 +54,10 @@ const (
 	cfgLoggerSamplingThereafter = "logger.sampling.thereafter"
 
 	// Uploader Header
-	cfgUploaderHeader    = "uploader_header"
-	cfgUploaderHeaderKey = "key"
-	cfgUploaderHeaderVal = "val"
+	cfgUploaderHeader                       = "uploader_header"
+	cfgUploaderHeaderKey                    = "key"
+	cfgUploaderHeaderVal                    = "val"
+	cfgUploaderHeaderEnableDefaultTimestamp = "upload_header.use_default_timestamp"
 
 	// Peers
 	cfgPeers = "peers"
@@ -144,6 +145,9 @@ func settings() *viper.Viper {
 	v.SetDefault(cfgWebWriteTimeout, time.Minute)
 	v.SetDefault(cfgWebConnectionPerHost, 10)
 
+	// upload header
+	v.SetDefault(cfgUploaderHeaderEnableDefaultTimestamp, false)
+
 	if err := v.BindPFlags(flags); err != nil {
 		panic(err)
 	}