[REQ] [csharp] Remove DataContract from model

[yuxinbo]

I want to inherit from Model generated by openapi generator, then I found the new property always null because it doesn't have DataMember attribute and since this Model is declared with DataContract attribute, it would serialize by DataContract & DataMember. This requires the inherit class also has DataMember attribute with new property. That isn't convenient to always ask used project to know this rule and it is better to let Web Application to config what is the serialize and deserialize rule for Json.

It is better to have the option to remove DataContract & DataMember attribute.