Add game.time_scale cvar

Primary use case (other than silly) is to be a better way to speed up/slow down replays.

Robust.Server/BaseServer.cs

@@ -594,6 +594,19 @@ namespace Robust.Server
                 _logger.Info($"Tickrate changed to: {b} on tick {_time.CurTick}");
             });
 
+            _config.OnValueChanged(CVars.GameTimeScale, f =>
+            {
+                if (!GameTiming.IsTimescaleValid(f))
+                {
+                    _logger.Error($"Invalid time scale set: {f}, ignoring");
+                    return;
+                }
+
+                _time.TimeScale = f;
+
+                _logger.Info($"Timescale changed to: {f} on tick {_time.CurTick}");
+            }, true);
+
             var startOffset = TimeSpan.FromSeconds(_config.GetCVar(CVars.NetTimeStartOffset));
             _time.TimeBase = (startOffset, GameTick.First);
             _time.TickRate = (ushort) _config.GetCVar(CVars.NetTickrate);