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/development/strategies/override-strategy.md

@@ -11,7 +11,7 @@ In this document, you’ll learn how to override a strategy in a Medusa backend
 
 The Medusa core defines and uses strategies for certain functionalities, which allows developers to override these functionalities and implement them as fits for their use case.
 
-For example, the cart completion process is implemented within a `CartCompletionStrategy` that is used inside the Complete Cart endpoint. If you need to change the cart completion process, you can override the `CartCompletionStrategy` and implement your own strategy. The Medusa backend will then use your strategy instead of the one defined in the core.
+For example, the cart completion process is implemented within a `CartCompletionStrategy` that is used inside the Complete Cart API Route. If you need to change the cart completion process, you can override the `CartCompletionStrategy` and implement your own strategy. The Medusa backend will then use your strategy instead of the one defined in the core.
 
 ### Hierarchy of Strategy Resolution
 

www/apps/docs/content/development/strategies/overview.mdx

@@ -15,9 +15,9 @@ A strategy is an isolated piece of business logic that can be overridden and cus
 
 For example, in the core `@medusajs/medusa` package, strategies are used to implement functionalities like cart completion and product import.
 
-These strategy classes are then resolved in endpoints, services, or wherever needed using dependency injection and used to perform their designated functionality.
+These strategy classes are then resolved in API Routes, services, or wherever needed using dependency injection and used to perform their designated functionality.
 
-For example, the `CartCompletionStrategy` is resolved in the Complete Cart endpoint that is defined in the core `@medusajs/medusa` package. It’s then used to complete the cart and place the order:
+For example, the `CartCompletionStrategy` is resolved in the Complete Cart API Route that is defined in the core `@medusajs/medusa` package. It’s then used to complete the cart and place the order:
 
 ```ts
 export default async (req, res) => {