listPlaylistsByUser(userId: string,requestingUserId: string | null,page: number,limit: number,sort: PlaylistSort,categoryId?: string): Page<Playlist>
Returns a page of userId's playlists, in the order sort names, for
GET /api/users/:key/playlists, optionally only those in the playlist
category categoryId. The private ones are listed only when
requestingUserId is userId.
sort: PlaylistSort