Retain message fields in the same order as defined in the .proto file

[MalitsPlus]

While fields in the json string output by protojson are kept in the same order as defined in the .proto file, fields in the yaml string output by protoyaml-go are sorted alphabetically.
This can be a little unfriendly to human reading in some cases. (e.g. We usually define the first field as "id", if sorted alphabetically we will have to scroll down a long way to find it)

It will be very appreciate if protoyaml-go provides an option to let users choose to keep the original order or not.