docs : fix variable assignment and importing PostRepository (#4286)

* fix variable assignment and import in step-5

* update with postRepository_ suffix for flexibility and avoiding name conflicts

* fixed ESLint Errors

docs/content/development/entities/create.md

@@ -136,18 +136,21 @@ You can access your custom entity data in the database in services or subscriber
 
 ```ts
 import { TransactionBaseService } from "@medusajs/medusa"
+import PostRepository from "../repositories/post"
 
 class PostService extends TransactionBaseService {
+  protected readonly postRepository_: typeof PostRepository
+  
   constructor({ postRepository, manager }) {
     super({ postRepository, manager })
 
-    this.postRepository = postRepository
+    this.postRepository_ = postRepository
     this.manager_ = manager
   }
 
   async list() {
     const postRepo = this.manager_
-      .withRepository(this.postRepository)
+      .withRepository(this.postRepository_)
     return await postRepo.find()
   }
 }