[FEATURE REQUEST]: Add AwaitTerminationAsync for StreamingQuery

[SWATOPLUS]

I am wanna to mange with many StreamingQuery in single spark job. So adding a AwaitTerminationAsync method should resolve this problem.

The example solution

        private static async Task AwaitTerminationAsync(StreamingQuery query, CancellationToken token)
        {
            while (query.IsActive())
            {
                await Task.Delay(100, token);

                if (token.IsCancellationRequested)
                {
                    query.Stop();
                }
            }

            var ex = query.Exception();

            if (ex != null)
            {
                throw ex;
            }
        }

[imback82]

@SWATOPLUS we only expose APIs that are already available on the Java/Scala side. This can be just added in your application as needed?

[SWATOPLUS]

I think it will be good if you found some other way to complete the task, instead of Delay. Maybe java api has some callback registration. and so on. Yeah this is not hottest feature, but it need to be implemented in dotnet way.