[MM-59519] preserve DM/GM unread/read state over export and import (#27707)

server/public/model/channel.go

@@ -122,7 +122,7 @@ type ChannelForExport struct {
 
 type DirectChannelForExport struct {
 	Channel
-	Members *[]string
+	Members []*ChannelMemberForExport
 }
 
 type ChannelModeration struct {