fix: add msg transfer main file

cmd/openim-msgtransfer/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"github.com/OpenIMSDK/Open-IM-Server/pkg/common/cmd"
+)
+
+func main() {
+	msgTransferCmd := cmd.NewMsgTransferCmd()
+	msgTransferCmd.AddPrometheusPortFlag()
+	if err := msgTransferCmd.Exec(); err != nil {
+		panic(err.Error())
+	}
+}