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/routes/preferences.cr

@@ -144,6 +144,8 @@ module Invidious::Routes::PreferencesRoute
     notifications_only ||= "off"
     notifications_only = notifications_only == "on"
 
+    default_playlist = env.params.body["default_playlist"]?.try &.as(String)
+
     # Convert to JSON and back again to take advantage of converters used for compatibility
     preferences = Preferences.from_json({
       annotations:                 annotations,
@@ -180,6 +182,7 @@ module Invidious::Routes::PreferencesRoute
       vr_mode:                     vr_mode,
       show_nick:                   show_nick,
       save_player_pos:             save_player_pos,
+      default_playlist:            default_playlist,
     }.to_json)
 
     if user = env.get? "user"