start of persistence support (#20770)

Co-authored-by: deltanedas <@deltanedas:kde.org>

Content.Shared/CCVar/CCVars.cs

@@ -179,6 +179,19 @@ namespace Content.Shared.CCVar
         public static readonly CVarDef<string>
             GameMap = CVarDef.Create("game.map", string.Empty, CVar.SERVERONLY);
 
+        /// <summary>
+        ///     Controls whether to use world persistence or not.
+        /// </summary>
+        public static readonly CVarDef<bool>
+            UsePersistence = CVarDef.Create("game.usepersistence", false, CVar.ARCHIVE);
+
+        /// <summary>
+        ///     If world persistence is used, what map prototype should be initially loaded.
+        ///     If the save file exists, it replaces MapPath but everything else stays the same (station name and such).
+        /// </summary>
+        public static readonly CVarDef<string>
+            PersistenceMap = CVarDef.Create("game.persistencemap", "Empty", CVar.ARCHIVE);
+
         /// <summary>
         ///     Prototype to use for map pool.
         /// </summary>