Add graceful handling for OperationCanceledException in Client

[nothrow]

Is your feature request related to a problem? Please describe.

When there is cancellation during reading from stream, two log messages of "fail" level are emitted. This happens for any request that returns stream.

var cancellationTokenSource = new CancellationTokenSource(5000);
var client = new MetadataService.MetadataServiceClient(_channel);
using var subscription = client.WatchChanges(new Empty()); // this is just for demonstration, I don't think proto is necessary
await foreach (var change in subscription.ResponseStream.ReadAllAsync(cancellationTokenSource.Token))
                            {
                                Console.WriteLine(change.Elements.Count);
                            }

fail: Grpc.Net.Client.Internal.GrpcCall[17]
      Error reading message.
System.Threading.Tasks.TaskCanceledException: The operation was canceled.
   at System.Net.Http.CancellationHelper.ThrowOperationCanceledException(Exception innerException, CancellationToken cancellationToken)
   at System.Net.Http.CancellationHelper.ThrowIfCancellationRequested(CancellationToken cancellationToken)
   at System.Net.Http.Http2Connection.Http2Stream.GetCancelableWaiterTask(CancellationToken cancellationToken)
   at System.Net.Http.Http2Connection.Http2Stream.ReadDataAsync(Memory`1 buffer, HttpResponseMessage responseMessage, CancellationToken cancellationToken)
   at Grpc.Net.Client.StreamExtensions.ReadMessageAsync[TResponse](Stream responseStream, ILogger logger, Func`2 deserializer, String grpcEncoding, Nullable`1 maximumMessageSize, Dictionary`2 compressionProviders, Boolean singleMessage, CancellationToken cancellationToken)
fail: Grpc.Net.Client.Internal.GrpcCall[3]
      Call failed with gRPC error status. Status code: 'Cancelled', Message: 'gRPC call disposed.'.

Describe the solution you'd like

I believe cancelling should not have 'fail' severity - I suggest debug is enough. This issue floods my logs on shutdown of the service, and I find it annoying.

Fixing this specific instance is pretty easy and I can PR it, I would, however, like, to suggest some more organized effort in graceful handling of cancellation.

Describe alternatives you've considered

Grpc.Core does not suffer from this flaw. I switched, for client, to Grpc.Core for now.

[JamesNK]

This is already fixed #697

You can wait until the next release or use a nightly package from the NuGet feed. Instructions: https://github.com/grpc/grpc-dotnet#grpc-nuget-feed

[JamesNK]

Actually, that issue was on the server. Let me test what happens in the client.

[nothrow]

https://github.com/grpc/grpc-dotnet/blob/master/src/Grpc.Net.Client/Internal/StreamExtensions.cs#L176

Here it looks like there is no special case for cancellation, and client just log everything.