docs(openapi) fix reusable custom decorator explanation

Ensure that when creating a reusable decorator `SwaggerModule` will create a definition for the
used model by adding it as an extra model in the definition of the decorator.

Author: Uros Kukic

content/openapi/operations.md

@@ -258,6 +258,7 @@ export const ApiPaginatedResponse = <TModel extends Type<any>>(
   model: TModel,
 ) => {
   return applyDecorators(
+    ApiExtraModels(model),
     ApiOkResponse({
       schema: {
         allOf: [
@@ -279,6 +280,8 @@ export const ApiPaginatedResponse = <TModel extends Type<any>>(
 
 > info **Hint** `Type<any>` interface and `applyDecorators` function are imported from the `@nestjs/common` package.
 
+To ensure that `SwaggerModule` will generate a definition for our model, we must add it as an extra model, like we did earlier with the `PaginatedDto` in the controller.
+
 With this in place, we can use the custom `@ApiPaginatedResponse()` decorator on our endpoint:
 
 ```ts