Improved C# grpc server implementation to be able to register call handlers

Move pollset_kick wfd creation/destruction out of freelist lock

This was an observed source of contention at higher thread counts where
we could overrun the freelist cap.

Adding support for loading the SSL roots from an environment variable.

Added usage info to csharp/README.md

Fix some memory leaks

Docker

Prevents a use-after-free

Prototype of gRPC C# library (Core and API examples)

Added a lot more information to Node README