[#237] pool: Return creation epoch from object put

Signed-off-by: Marina Biryukova <m.biryukova@yadro.com>

object/transformer/transformer.go

@@ -247,6 +247,7 @@ func (s *payloadSizeLimiter) fillHeader() (*AccessIdentifiers, error) {
 		ParentID:     parID,
 		SelfID:       id,
 		ParentHeader: parHdr,
+		Epoch:        curEpoch,
 	}, nil
 }
 

object/transformer/types.go

@@ -14,6 +14,7 @@ type AccessIdentifiers struct {
 	ParentID     *oid.ID
 	SelfID       oid.ID
 	ParentHeader *object.Object
+	Epoch        uint64
 }
 
 // EpochSource is a source for the current epoch.