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/plugins/notifications/twilio-sms.md

@@ -55,7 +55,7 @@ Make sure to replace `<YOUR_ACCOUNT_SID>`, `<YOUR_AUTH_TOKEN>`, and `<YOUR_TWILI
 
 Finally, add the plugin and its options in the `medusa-config.js` file to the `plugins` array:
 
-```jsx title=medusa-config.js
+```js title=medusa-config.js
 const plugins = [
   // ...
   {
@@ -85,7 +85,7 @@ For this example to work, you'll need to have an event bus module installed and
 
 Create the file `src/services/sms.js` in your Medusa backend with the following content:
 
-```jsx title=src/services/sms.js
+```js title=src/services/sms.js
 class SmsSubscriber {
   constructor({ 
     twilioSmsService,