New Objective: Ensure another traitor stays alive. (#6020)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>
Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.Server/Objectives/Requirements/MultipleTraitorsRequirement.cs

@@ -0,0 +1,21 @@
+using System;
+using Content.Server.Objectives.Interfaces;
+using Content.Server.Traitor;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Robust.Shared.GameObjects;
+using Content.Server.GameTicking.Rules;
+
+namespace Content.Server.Objectives.Requirements
+{
+    [DataDefinition]
+    public class MultipleTraitorsRequirement : IObjectiveRequirement
+    {
+        [DataField("traitors")]
+        private readonly int _requiredTraitors = 2;
+
+        public bool CanBeAssigned(Mind.Mind mind)
+        {
+            return EntitySystem.Get<TraitorRuleSystem>().TotalTraitors >= _requiredTraitors;
+        }
+    }
+}