Stories - user provided, shorter lifetime contributions

[gnunicorn]

Rust Side is implemented, see Story and Client.latestStories, equivalent to News. The UI has been agreed upon to be just minimal changes compared to the existing News-Feature, showing all of the updates in the same updates stream.

As the API is almost identical and only minor differences exist, there is a case to be made to refactor the existing Widgets to use an abstract UpdateEntry type that both types can just be wrapped into.

[gnunicorn]

Ref lifetime matrix-org/matrix-spec-proposals#2228