Return HTTP 204 instead of 404 for empty tiles

[stevage]

Mapbox-GL-JS generates a lot of error messages when receiving 404 messages from Tessera, and apparently the recommended solution is for the tile server to send HTTP 204 instead of 404.

Could that be an option, or perhaps even the default?

(This is specifically for the case where tiles exist for the given URL, but not the specific tile requested.)