* Replace request by fetch
* Promisify NotificationsHandler.js
* Replace to `fetchNothing` when we don't consume the body.
I also checked that these endpoints don't return anything: https://github.com/overleaf/internal/blob/de2d0ed8cab15c4347ddecf227073a6d4e06120f/services/notifications/app.js
* Make URLs safer
* Ignore (but log) failing `fetchNothing`s on DELETE endpoints
* Defensively add `userId.toString()` to prevent bugs (!)
* Update NotificationsHandler unit tests
* Throw fetch errors only if we did not get a response
GitOrigin-RevId: 03700ad29658c0e3af4e476b25a964030e9c97f1
Antoine Clausse