Passed to PUT /api/playlists/:playlistId by PlaylistDetail. A field left
out keeps its value.
optional
title: string
optional
slug: string
A new slug, which the edit form's slug field sends. A title change never changes the slug by itself.
optional
description: string | null
null removes the description.
optional
isPublic: boolean
optional
categoryIds: string[]
Replaces its playlist categories; [] takes it out of every one.