Adds a cvar for server rules (#8365)

Co-authored-by: Veritius <veritiusgaming@gmail.com>
Co-authored-by: ike709 <ike709@github.com>

Content.Shared/CCVar/CCVars.cs

@@ -17,6 +17,12 @@ namespace Content.Shared.CCVar
         public static readonly CVarDef<string> ServerId =
             CVarDef.Create("server.id", "unknown_server_id", CVar.REPLICATED | CVar.SERVER);
 
+        /// <summary>
+        ///     Name of the rules txt file in the "Resources/Server Info" dir. Include the extension.
+        /// </summary>
+        public static readonly CVarDef<string> RulesFile =
+            CVarDef.Create("server.rules_file", "Rules.txt", CVar.REPLICATED | CVar.SERVER);
+
         /*
          * Ambience
          */