Activity Tracking extension should implement the `onServerDelete` method to prompt the server admin whether they want to delete all their data

[tomli380576]

When a server is deleted or YABOB is kicked from the server, the server owner has no way of asking YABOB to delete all the attendance tracking data from firebase. The extension should implement the onServerDelete method to prompt the server owner whether they want to delete data and actually execute the deletion once they confirm