allow custom codegen generator be loaded

Author: HugoMario

modules/swagger-codegen/src/main/java/io/swagger/codegen/v3/config/CodegenConfigurator.java

@@ -515,7 +515,7 @@ public ClientOptInput toClientOptInput() {
         setVerboseFlags();
         setSystemProperties();
 
-        CodegenConfig config = CodegenConfigLoader.forName(lang);
+        CodegenConfig config = loadCodegenConfig();
         ClientOptInput input = new ClientOptInput();
 
         Predicate<URL> urlMatcher = null;
@@ -669,6 +669,10 @@ public ClientOptInput toClientOptInput() {
         return input;
     }
 
+    protected CodegenConfig loadCodegenConfig() {
+        return CodegenConfigLoader.forName(lang);
+    }
+
     private ParseOptions buildParseOptions() {
         ParseOptions options = new ParseOptions();
         options.setResolve(true);