Add CancellationToken Support for Retry

[blatybus]

Retry does not support CancellationToken at the moment. Something like this would be nice to have so that retries can be cancelled:

public static TResult Retry(
Func<CancellationToken, TResult> producer,
Func<Exception, bool> shouldRetry,
IRetryPolicy retryPolicy,
CancellationToken cancellationToken = default)
{
var retryCount = 0;

while (true)
{
    cancellationToken.ThrowIfCancellationRequested();

    try
    {
        return producer(cancellationToken);
    }
    catch (Exception exception)
        when (shouldRetry(exception) && retryCount < retryPolicy.MaxRetries)
    {
        retryCount++;

        Task.Delay(retryPolicy.Delay(retryCount), cancellationToken)
            .GetAwaiter()
            .GetResult();
    }
}

}