Support retrieval of _current snapshot status #80931
Description
Today the get snapshot status docs indicate that it's expensive to retrieve the status of completed snapshots and suggests that you can use the string _current to retrieve currently-running snapshots. It's true that getting the status of completed snapshots is expensive, but it's not true that you can use _current in this way: that only works for the get snapshots API. However it would be awfully useful to support this feature in the snapshot status API too, seeing as how getting the status of currently-running snapshots is the cheapest way to use this API.
(you can use GET _snapshot/my_repository/_status to get the status of all running snapshots, but this is undocumented today which needs addressing too)