Port new CosmosDB Partitioned Storage from C#

[garypretty]

A new Cosmos DB storage implementation which utilizes the v3 API and handles the partition key internally has been implemented in C#.

C# implementation is here microsoft/botbuilder-dotnet#2613

[mdrichardson]

Just FYI to anybody that might want to jump on this. I'm writing the tests for this right now. It's going to take a bit as I'll also write a Storage Base Tests class, similar to this PR