fix schema generation to allow proper types in front

Now frontend relies on propres schema generation. Issues to fix :

• Artist cover : !2895 (merged)
• Description field for track and album : !2894 (merged)
• Album.tracks :
• tags on artist
• Artist instead of SimpleArtist
• cover.urls.[specified]
• playlist, radio, podcasts, series on search endpoint are missing (not a schema problem, to do later)

to test : docker compose run --rm api funkwhale-manage spectacular > ./schema.lol