ZitiContext should also take a stream/byte array

[dovholuknf]

The c sdk zitilib allows for Ziti_load_context to pass a pointer that represents either json or a path on the file system. Expose this capability to .NET consumers by allowing something like:

        public ZitiContext(byte[] identity) {
            NativeContext = nAPI.Ziti_load_context(identity);
        }