docs: update endpoints to use file-routing approach (#5397)

- Move the original guides for creating endpoints and middlewares to sub-sections in the Endpoints category.
- Replace existing guides for endpoints and middlewares with the new approach.
- Update all endpoints-related snippets across docs to use this new approach.

www/apps/docs/content/troubleshooting/awilix-resolution-error/_custom-registration.md

@@ -24,4 +24,4 @@ class CustomService extends TransactionBaseService {
 export default CustomService
 ```
 
-You can learn more about this in the [Middlewares documentation](../../development/endpoints/add-middleware.mdx).
+You can learn more about this in the [Middlewares documentation](../../development/api-routes/add-middleware.mdx).