feat(auth): add rate limiting middleware to request code endpoint

- Implement rate limiting specifically for the `/api/v1/auth/request-code` endpoint
- Use custom rate limit configuration from EnvironmentConfig
- Apply rateLimiter middleware with ipKeyExtractor for key generation

Author: fulleni

routes/api/v1/auth/request-code/_middleware.dart

@@ -0,0 +1,15 @@
+import 'package:dart_frog/dart_frog.dart';
+import 'package:flutter_news_app_api_server_full_source_code/src/config/environment_config.dart';
+import 'package:flutter_news_app_api_server_full_source_code/src/middlewares/rate_limiter_middleware.dart';
+
+/// This middleware applies a rate limit specifically to the
+/// `/api/v1/auth/request-code` endpoint.
+Handler middleware(Handler handler) {
+  return handler.use(
+    rateLimiter(
+      limit: EnvironmentConfig.rateLimitRequestCodeLimit,
+      window: EnvironmentConfig.rateLimitRequestCodeWindow,
+      keyExtractor: ipKeyExtractor,
+    ),
+  );
+}