FunctionRpc proto file defines: [WorkerTerminate ](https://github.com/Azure/azure-functions-host/blob/a32a63925c9e67a4ce1af4a49ae1dd3b16d7f7e2/src/WebJobs.Script.Grpc/azure-functions-language-worker-protobuf/src/proto/FunctionRpc.proto#L160-L162). Need to update host to send WorkerTerminate message with a grace period.