Add cvar for events (#2478)

There's also the existing events command as well that's separate. I think there's value in having both? (Where mods can turn it on and off but not change the default?)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Shared/CCVars.cs

@@ -7,6 +7,9 @@ namespace Content.Shared
     [CVarDefs]
     public sealed class CCVars : CVars
     {
+        public static readonly CVarDef<bool>
+            EventsEnabled = CVarDef.Create("events.enabled", false, CVar.ARCHIVE | CVar.SERVERONLY);
+
         public static readonly CVarDef<bool>
             GameLobbyEnabled = CVarDef.Create("game.lobbyenabled", false, CVar.ARCHIVE);