The FolderWatchStateChanged event is emitted when a folder's watcher routine
encounters a new error, or when a previous error disappeared after retrying.
The event contains the ID of the affected folder and textual error messages
describing the previous (from) and the updated (to) error conditions.
If there was no error in either of these, the respective field is omitted.
{
"id": 123,
"type": "FolderWatchStateChanged",
"time": "2022-03-14T12:34:56.890000000+01:00",
"data": {
"folder": "default",
"from": "Something bad happened.",
"to": "Something worse happened."
}
}