Capture gRpc server logs in the host

[Grpc.Core.GrpcEnvironment](https://grpc.io/grpc/csharp/api/Grpc.Core.GrpcEnvironment.html) has a shutdown even that get fired when the shutdown happens. Functions host needs to be updated to listen for this event and log the reason for shutdown.
Currently, if the shutdown is initiated by the gRpc service, rpc channel is shutdown and any logs from the language workers are lost.