Modify admin chat (#13050)

* split admin chat into new channel

* add ability to play audio when a chat message is received and add audio to admin chat

* give client control of AdminChat sound and volume + suppress sound for senders

Content.Shared/Chat/ChatChannelExtensions.cs

@@ -12,6 +12,7 @@ public static class ChatChannelExtensions
             ChatChannel.OOC => Color.LightSkyBlue,
             ChatChannel.Dead => Color.MediumPurple,
             ChatChannel.Admin => Color.Red,
+            ChatChannel.AdminChat => Color.HotPink,
             ChatChannel.Whisper => Color.DarkGray,
             _ => Color.LightGray
         };