Docs: Change DELETE to POST in Related Questions curl example (#7054)

### What problem does this PR solve?

docs(api): Fix request method in Related Questions example (DELETE→POST)

### Type of change

- [x] Documentation Update

docs/references/http_api_reference.md

@@ -3169,7 +3169,7 @@ The chat model dynamically determines the number of questions to generate based
 ##### Request example
 
 ```bash
-curl --request DELETE \
+curl --request POST \
      --url http://{address}/api/v1/conversation/related_questions \
      --header 'Content-Type: application/json' \
      --header 'Authorization: Bearer <YOUR_API_KEY>' \