Adding the generator version template to api mustache file (#5691)

modules/swagger-codegen/src/main/resources/JavaSpring/api.mustache

@@ -1,3 +1,8 @@
+/**
+ * NOTE: This class is auto generated by the swagger code generator program ({{{generatorVersion}}}).
+ * https://github.com/swagger-api/swagger-codegen
+ * Do not edit the class manually.
+ */
 package {{package}};
 
 {{#imports}}import {{import}};