Based on roadmap discussion on Oct 29, 2019, creating this ticket to track adding metadata tracking to legacy API.

This will involve changes to MongoDB.Driver.Core.Connections.ClientDocumentHelper such that the driver name is not simply hard-coded to "mongo-charp-driver", but rather can have another string optionally appended to it.

So for users of the the MongoDB.Driver module, the name can stay the same. But for users of the MongoDB.Driver.Legacy module, it should be "mongo-csharp-driver|legacy".

See https://github.com/mongodb/specifications/blob/master/source/mongodb-handshake/handshake.rst for general information about the handshake protocol.