fix: Change Open API validation middleware to specify and use path parameters (#8913)

## About the changes
Moved Open API validation handler to the controller layer to reuse on
all services such as project and segments, and also removed unnecessary
middleware at the top level, `app.ts`, and method, `useErrorHandler` in
`openapi-service.ts`.

### Important files

#### Before

<img width="1510" alt="1 Before"
src="https://github.com/user-attachments/assets/96ac245d-92ac-469e-a097-c6c0b78d0def">

Express cant' parse the path parameter because it doesn't be specified
on the `use` method. Therefore, it returns `undefined` as an error
message.

#### After

<img width="1510" alt="2 After"
src="https://github.com/user-attachments/assets/501dae6c-fef5-4e77-94c3-128a9f7210da">

Express can parse the path parameter because I change to specify it on
the controller layer. Accordingly, it returns `test`.

src/lib/app.ts

@@ -197,10 +197,6 @@ export default async function getApp(
     // Setup API routes
     app.use(`${baseUriPath}/`, new IndexRouter(config, services, db).router);
 
-    if (services.openApiService) {
-        services.openApiService.useErrorHandler(app);
-    }
-
     if (process.env.NODE_ENV !== 'production') {
         app.use(errorHandler());
     } else {

src/lib/routes/controller.ts

@@ -10,6 +10,7 @@ import { type IUnleashConfig, NONE } from '../types';
 import { handleErrors } from './util';
 import requireContentType from '../middleware/content_type_checker';
 import { PermissionError } from '../error';
+import { fromOpenApiValidationErrors } from '../error/bad-data-error';
 import { storeRequestedRoute } from '../middleware/response-time-metrics';
 
 type IRequestHandler<P = any, ResBody = any, ReqBody = any, ReqQuery = any> = (
@@ -64,6 +65,16 @@ const checkPrivateProjectPermissions = () => async (req, res, next) => {
     return res.status(404).end();
 };
 
+const openAPIValidationMiddleware = async (err, req, res, next) => {
+    if (err?.status && err.validationErrors) {
+        const apiError = fromOpenApiValidationErrors(req, err.validationErrors);
+
+        res.status(apiError.statusCode).json(apiError);
+    } else {
+        next(err);
+    }
+};
+
 /**
  * Base class for Controllers to standardize binding to express Router.
  *
@@ -114,6 +125,8 @@ export default class Controller {
             this.useContentTypeMiddleware(options),
             this.useRouteErrorHandler(options.handler.bind(this)),
         );
+
+        this.app.use(options.path, openAPIValidationMiddleware);
     }
 
     get(

src/lib/services/openapi-service.ts

@@ -11,7 +11,6 @@ import type { ApiOperation } from '../openapi/util/api-operation';
 import type { Logger } from '../logger';
 import { validateSchema } from '../openapi/validate';
 import type { IFlagResolver } from '../types';
-import { fromOpenApiValidationErrors } from '../error/bad-data-error';
 
 export class OpenApiService {
     private readonly config: IUnleashConfig;
@@ -60,21 +59,6 @@ export class OpenApiService {
         });
     }
 
-    useErrorHandler(app: Express): void {
-        app.use((err, req, res, next) => {
-            if (err?.status && err.validationErrors) {
-                const apiError = fromOpenApiValidationErrors(
-                    req,
-                    err.validationErrors,
-                );
-
-                res.status(apiError.statusCode).json(apiError);
-            } else {
-                next(err);
-            }
-        });
-    }
-
     respondWithValidation<T, S = SchemaId>(
         status: number,
         res: Response<T>,