* Add BackgroundService, a base class for long running HostedServices
- Today the IHostedService pattern is a StartAsync/StopAsync pattern. Neither of these
methods are supposed to return a long running task that represents an execution. If
you wanted to have some logic run on a timer every 5 minutes, it's unnatural to do so
with simple async idioms. This base class implements IHostedService and exposes
a pattern where a long running async Task can be returned.
- The token passed into ExecuteAsync represents the lifetime of the execution.
- StartAsync and StopAsync were made virtual to allow the derived type to
indicate Start failures.
- Added tests
David Fowler
Chris Ross (ASP.NET)