RESTful API to return the latest shutdown events

@hectoratcasper commented on [Tue Mar 14 2023](https://github.com/CasperLabs/Solution-Architecture/issues/74)

https://docs.google.com/document/d/1vBRbBmij9HHotY_8HIaUKk5a9Kq9Rqgxlk-UAE_F7xs/edit?pli=1

The Shutdown event is emitted when the node is about to shut down, usually for an upgrade. This causes a termination of the event stream since the server is shutting down. The SSE sidecar stores this event in the shutdown table:


We require a new RESTful API for this event that would allow operators to get the latest node shutdown events filter by a limit:

```
/shutdown?limit=10
```

Start with the SSE sidecar's shutdown table and the existing REST API entry points. Check how shutdown events are stored and how limit query parameters are handled, then expose the latest shutdown events at the requested /shutdown?limit endpoint and verify the response behavior.

Written by the indexing model from the issue text.