refactor: Add stop_at_height option in ChainstateManager

Remove access to the global gArgs for the stopatheight argument and
replace it by adding a field to the existing ChainstateManager Options
struct.

This should eventually allow users of the ChainstateManager to not rely
on the global gArgs and instead pass in their own options.

src/node/chainstatemanager_args.cpp

@@ -37,6 +37,8 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& args, ChainstateManage
 
     if (auto value{args.GetIntArg("-maxtipage")}) opts.max_tip_age = std::chrono::seconds{*value};
 
+    if (auto value{args.GetIntArg("-stopatheight")}) opts.stop_at_height = *value;
+
     ReadDatabaseArgs(args, opts.block_tree_db);
     ReadDatabaseArgs(args, opts.coins_db);
     ReadCoinsViewArgs(args, opts.coins_view);