Added POST method to upload files into NeoFS through HTTP Gate

- Updated README
- Added method to upload files into NeoFS
- HTTP Upload Header Filter loaded from settings
- Added `HeaderFilter` that filters headers (object attributes)

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

settings.go

@@ -16,8 +16,7 @@ import (
 type empty int
 
 const (
-	devNull   = empty(0)
-	generated = "generated"
+	devNull = empty(0)
 
 	defaultRebalanceTimer = 15 * time.Second
 	defaultRequestTimeout = 15 * time.Second
@@ -54,6 +53,11 @@ const (
 	cfgLoggerSamplingInitial    = "logger.sampling.initial"
 	cfgLoggerSamplingThereafter = "logger.sampling.thereafter"
 
+	// Uploader Header
+	cfgUploaderHeader    = "uploader_header"
+	cfgUploaderHeaderKey = "key"
+	cfgUploaderHeaderVal = "val"
+
 	// Peers
 	cfgPeers = "peers"
 
@@ -179,6 +183,13 @@ func settings() *viper.Viper {
 		fmt.Printf("%s_%s_[N]_ADDRESS = string\n", Prefix, strings.ToUpper(cfgPeers))
 		fmt.Printf("%s_%s_[N]_WEIGHT = 0..1 (float)\n", Prefix, strings.ToUpper(cfgPeers))
 
+		fmt.Println()
+		fmt.Println("Upload Header Table:")
+		fmt.Println()
+
+		fmt.Printf("%s_%s_[N]_%s = string\n", Prefix, strings.ToUpper(cfgUploaderHeader), strings.ToUpper(cfgUploaderHeaderKey))
+		fmt.Printf("%s_%s_[N]_%s = string\n", Prefix, strings.ToUpper(cfgUploaderHeader), strings.ToUpper(cfgUploaderHeaderVal))
+
 		os.Exit(0)
 	case version != nil && *version:
 		fmt.Printf("NeoFS HTTP Gateway %s (%s)\n", Version, Build)