Add default playlist preference (#5449)

* Add default playlist preference

Closes https://github.com/iv-org/invidious/issues/5421

* Add option to set default playlist to none

* Move it to player preferences

src/invidious/config.cr

@@ -52,6 +52,8 @@ struct ConfigPreferences
   property vr_mode : Bool = true
   property show_nick : Bool = true
   property save_player_pos : Bool = false
+  @[YAML::Field(ignore: true)]
+  property default_playlist : String? = nil
 
   def to_tuple
     {% begin %}