Add support for specifying an [SSL cert to use when connecting to Mongo](https://mongodb.github.io/mongo-csharp-driver/2.10/reference/driver/ssl/). Perhaps more broadly allow configuration of [MongoClientSettings](https://mongodb.github.io/mongo-csharp-driver/2.10/apidocs/html/T_MongoDB_Driver_MongoClientSettings.htm) or allow the application to create the MongoClient instance via a callback method.