Release 1.0.0-alpha04

Release the .NET Functions Framework 1.0.0-alpha04

Changes since 1.0.0-alpha03

- BREAKING: ICloudEventFunction.HandleAsync now accepts a CancellationToken
- Feature: CloudEventAdapter logs requests that don't contain Cloud events
- Feature: robots.txt and favicon.ico requests do not invoke the function, instead returning 404
- Feature: Legacy event functions, with built-in payload types for Storage, Firestore and PubSub
- Feature: C# template for legacy events (other languages coming later)
- Fix: Exceptions are now logged in the simple console logger
- Fix: NuGet packages now have working SourceLink and deterministic source paths