fix: lobby music volume will be changed on options change without restart (also lobby music not looped anymore) (#25530)

* fix: lobby music volume will be changed on options change without restart (also lobby music not looped anymore)

* refactor: now lobby music is part of ContentAudioSystem. Lobby playlist is used instead of single track. Client now selects next lobby soundtrack after previous finished.

* refactor: incapsulated info on current lobby track in simple record

* refactor: fixed inconsistent naming between song and soundtrack for lobbymusic

* refactor: xml-doc for LobbyPlaylistChangedEvent

* fix: inverted invalid _audio.PlayGlobal check to return only if lobby soundtrack play call failed

---------

Co-authored-by: pa.pecherskij <pa.pecherskij@interfax.ru>

Content.Shared/Audio/Events/LobbyPlaylistChangedEvent.cs

@@ -0,0 +1,29 @@
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Audio.Events;
+
+/// <summary>
+/// Event of changing lobby music playlist (on server).
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class LobbyPlaylistChangedEvent : EntityEventArgs
+{
+    /// <inheritdoc />
+    public LobbyPlaylistChangedEvent(string[] playlist)
+    {
+        Playlist = playlist;
+    }
+
+    /// <summary>
+    /// List of soundtrack filenames for lobby playlist.
+    /// </summary>
+    public string[] Playlist;
+}
+
+/// <summary>
+/// Event of stopping lobby music.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class LobbyMusicStopEvent : EntityEventArgs
+{
+}