[TrueCloudLab#40] Add param to configure xml decoder

This parameter enables parsing xml body without
xmlns="http://s3.amazonaws.com/doc/2006-03-01/" attribute
for CompleteMultipartUpload requests

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/handler/api.go

@@ -1,7 +1,9 @@
 package handler
 
 import (
+	"encoding/xml"
 	"errors"
+	"io"
 	"time"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api"
@@ -26,6 +28,7 @@ type (
 	// Config contains data which handler needs to keep.
 	Config struct {
 		Policy             PlacementPolicy
+		XMLDecoder         XMLDecoderProvider
 		DefaultMaxAge      int
 		NotificatorEnabled bool
 		CopiesNumber       uint32
@@ -37,6 +40,10 @@ type (
 		Default() netmap.PlacementPolicy
 		Get(string) (netmap.PlacementPolicy, bool)
 	}
+
+	XMLDecoderProvider interface {
+		NewCompleteMultipartDecoder(io.Reader) *xml.Decoder
+	}
 )
 
 const (